[PATCH v1 0/5] Allocate cache entries from memory pool

[PATCH v1 0/5] Allocate cache entries from memory pool

[Jameson Miller]

This patch series improves the performance of loading indexes by
reducing the number of malloc() calls. Loading the index from disk is
partly dominated by the time in malloc(), which is called for each
index entry. This patch series reduces the number of times malloc() is
called as part of loading the index, and instead allocates a block of
memory upfront that is large enough to hold all of the cache entries,
and chunks this memory itself. This change builds on [1], which is a
prerequisite for this change.

Git previously allocated block of memory for the index cache entries
until [2].

This 5 part patch series is broken up as follows:

  1/5, 2/5 - Move cache entry lifecycle methods behind an API

  3/5 - Fill out memory pool API to include lifecycle and other
      	methods used in later patches

  4/5 - Allocate cache entry structs from memory pool

  5/5 - Add extra optional validation

Performance Benchmarks:

To evaluate the performance of this approach, the p0002-read-cache.sh
test was run with several combinations of allocators (glibc default,
tcmalloc, jemalloc), with and without block allocation, and across
several different index sized (100K, 1M, 2M entries). The details on
how these repositories were constructed can be found in [3].The
p0002-read-cache.sh was run with the iteration count set to 1 and
$GIT_PERF_REPEAT_COUNT=10.

The tests were run with iteration count set to 1 because this best
approximates the real behavior. The read_cache/discard_cache test will
load / free the index N times, and the performance of this logic is
different between N = 1 and N > 1. As the production code does not
read / discard the index in a loop, a better approximation is when N =
1.

100K

Test                                       baseline [4]       block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)    0.02(0.01+0.01) -33.3%

1M:

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)    0.17(0.07+0.09) -26.1%

2M:

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)    0.39(0.17+0.20) -13.3%


100K is not a large enough sample size to show the perf impact of this
change, but we can see a perf improvement with 1M and 2M entries. For
completeness, here is the p0002-read-cache tests for git.git and
linux.git:

git.git:

Test                                          baseline          block_allocation
 ---------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   0.30(0.26+0.03)   0.17(0.13+0.03) -43.3%

linux.git:

Test                                          baseline          block_allocation
 ---------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   7.05(6.01+0.84)   4.61(3.74+0.66) -34.6% 


We also investigated the performance of just using different
allocators. We can see that there is not a consistent performance
gain.

100K

Test                                       baseline [4]      tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)   0.03(0.01+0.01) +0.0%     0.03(0.02+0.01) +0.0% 

1M:

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)   0.21(0.10+0.10) -8.7%     0.27(0.16+0.10) +17.4%

2M:

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)   0.46(0.25+0.21) +2.2%     0.57(0.36+0.21) +26.7%


[1] https://public-inbox.org/git/20180321164152.204869-1-jamill@microsoft.com/

[2] debed2a629 (read-cache.c: allocate index entries individually - 2011-10-24)

[3] Constructing test repositories:

The test repositories were constructed with t/perf/repos/many_files.sh with the following parameters:

100K:	 many-files.sh 4 10 9
1M:	 many-files.sh 5 10 9
2M:	 many-files.sh 6 8 7

[4] baseline commit: 8b026eda Revert "Merge branch 'en/rename-directory-detection'"

Jameson Miller (5):
  read-cache: teach refresh_cache_entry to take istate
  Add an API creating / discarding cache_entry structs
  mem-pool: fill out functionality
  Allocate cache entries from memory pools
  Add optional memory validations around cache_entry lifecyle

 apply.c                |  26 +++---
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   8 +-
 builtin/reset.c        |   6 +-
 builtin/update-index.c |  26 +++---
 cache.h                |  40 ++++++++-
 git.c                  |   3 +
 mem-pool.c             | 136 ++++++++++++++++++++++++++++-
 mem-pool.h             |  34 ++++++++
 merge-recursive.c      |   4 +-
 read-cache.c           | 229 +++++++++++++++++++++++++++++++++++++++----------
 resolve-undo.c         |   6 +-
 split-index.c          |  31 +++++--
 tree.c                 |   4 +-
 unpack-trees.c         |  27 +++---
 16 files changed, 476 insertions(+), 117 deletions(-)


base-commit: cafaccae98f749ebf33495aec42ea25060de8682
-- 
2.14.3

[PATCH v1 0/5] Allocate cache entries from memory pool

[Jameson Miller]

This patch series improves the performance of loading indexes by
reducing the number of malloc() calls. Loading the index from disk is
partly dominated by the time in malloc(), which is called for each
index entry. This patch series reduces the number of times malloc() is
called as part of loading the index, and instead allocates a block of
memory upfront that is large enough to hold all of the cache entries,
and chunks this memory itself. This change builds on [1], which is a
prerequisite for this change.

Git previously allocated block of memory for the index cache entries
until [2].

This 5 part patch series is broken up as follows:

  1/5, 2/5 - Move cache entry lifecycle methods behind an API

  3/5 - Fill out memory pool API to include lifecycle and other
      	methods used in later patches

  4/5 - Allocate cache entry structs from memory pool

  5/5 - Add extra optional validation

Performance Benchmarks:

To evaluate the performance of this approach, the p0002-read-cache.sh
test was run with several combinations of allocators (glibc default,
tcmalloc, jemalloc), with and without block allocation, and across
several different index sized (100K, 1M, 2M entries). The details on
how these repositories were constructed can be found in [3].The
p0002-read-cache.sh was run with the iteration count set to 1 and
$GIT_PERF_REPEAT_COUNT=10.

The tests were run with iteration count set to 1 because this best
approximates the real behavior. The read_cache/discard_cache test will
load / free the index N times, and the performance of this logic is
different between N = 1 and N > 1. As the production code does not
read / discard the index in a loop, a better approximation is when N =
1.

100K

Test                                       baseline [4]       block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)    0.02(0.01+0.01) -33.3%

1M:

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)    0.17(0.07+0.09) -26.1%

2M:

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)    0.39(0.17+0.20) -13.3%


100K is not a large enough sample size to show the perf impact of this
change, but we can see a perf improvement with 1M and 2M entries.

For completeness, here is the p0002-read-cache tests for git.git and
linux.git:

git.git:

Test                                          baseline [4]     block_allocation
 ---------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   0.30(0.26+0.03)   0.17(0.13+0.03) -43.3%

linux.git:

Test                                          baseline          block_allocation
 ---------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   7.05(6.01+0.84)   4.61(3.74+0.66) -34.6% 


We also investigated the performance of just using different
allocators. We can see that there is not a consistent performance
gain.

100K

Test                                       baseline [4]      tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)   0.03(0.01+0.01) +0.0%     0.03(0.02+0.01) +0.0% 

1M:

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)   0.21(0.10+0.10) -8.7%     0.27(0.16+0.10) +17.4%

2M:

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)   0.46(0.25+0.21) +2.2%     0.57(0.36+0.21) +26.7%



[1] https://public-inbox.org/git/20180321164152.204869-1-jamill@microsoft.com/

[2] debed2a629 (read-cache.c: allocate index entries individually - 2011-10-24)

[3] Constructing test repositories:

The test repositories were constructed with t/perf/repos/many_files.sh with the following parameters:

100K:	 many-files.sh 4 10 9
1M:	 many-files.sh 5 10 9
2M:	 many-files.sh 6 8 7

[4] baseline commit: 8b026eda Revert "Merge branch 'en/rename-directory-detection'"

Jameson Miller (5):
  read-cache: teach refresh_cache_entry to take istate
  Add an API creating / discarding cache_entry structs
  mem-pool: fill out functionality
  Allocate cache entries from memory pools
  Add optional memory validations around cache_entry lifecyle

 apply.c                |  26 +++---
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   8 +-
 builtin/reset.c        |   6 +-
 builtin/update-index.c |  26 +++---
 cache.h                |  40 ++++++++-
 git.c                  |   3 +
 mem-pool.c             | 136 ++++++++++++++++++++++++++++-
 mem-pool.h             |  34 ++++++++
 merge-recursive.c      |   4 +-
 read-cache.c           | 229 +++++++++++++++++++++++++++++++++++++++----------
 resolve-undo.c         |   6 +-
 split-index.c          |  31 +++++--
 tree.c                 |   4 +-
 unpack-trees.c         |  27 +++---
 16 files changed, 476 insertions(+), 117 deletions(-)


base-commit: cafaccae98f749ebf33495aec42ea25060de8682
-- 
2.14.3

[PATCH v1 1/5] read-cache: teach refresh_cache_entry to take istate

[Jameson Miller]

Refactoring dependencies of make_cache_entry to work on a specific
index, instead of implicitly using the_index. This is in preparation
for making the make_cache_entry function work on a specific index.
---
 cache.h           | 2 +-
 merge-recursive.c | 2 +-
 read-cache.c      | 7 ++++---
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/cache.h b/cache.h
index bbaf5c349a..e50a847aea 100644
--- a/cache.h
+++ b/cache.h
@@ -743,7 +743,7 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 #define REFRESH_IGNORE_SUBMODULES	0x0010	/* ignore submodules */
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
-extern struct cache_entry *refresh_cache_entry(struct cache_entry *, unsigned int);
+extern struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 /*
  * Opportunistically update the index but do not complain if we can't.
diff --git a/merge-recursive.c b/merge-recursive.c
index 0c0d48624d..693f60e0a3 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -260,7 +260,7 @@ static int add_cacheinfo(struct merge_options *o,
 	if (refresh) {
 		struct cache_entry *nce;
 
-		nce = refresh_cache_entry(ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		nce = refresh_cache_entry(&the_index, ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
 		if (!nce)
 			return err(o, _("addinfo_cache failed for path '%s'"), path);
 		if (nce != ce)
diff --git a/read-cache.c b/read-cache.c
index 10f1c6bb8a..2cb4f53b57 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -767,7 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	ce->ce_namelen = len;
 	ce->ce_mode = create_ce_mode(mode);
 
-	ret = refresh_cache_entry(ce, refresh_options);
+	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
 		free(ce);
 	return ret;
@@ -1448,10 +1448,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	return has_errors;
 }
 
-struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+					       struct cache_entry *ce,
 					       unsigned int options)
 {
-	return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
-- 
2.14.3

Re: [PATCH v1 1/5] read-cache: teach refresh_cache_entry to take istate

[Ben Peart]

On 4/17/2018 12:34 PM, Jameson Miller wrote:
> Refactoring dependencies of make_cache_entry to work on a specific

Refactoring/Refactor

It's helpful to refer to functions with parens i.e. make_cache_entry().

In addition, it appears you only needed to update refresh_cache_entry() 
so perhaps something like:


Refactor refresh_cache_entry() to work on a specific index, instead of 
implicitly using the_index. This is in preparation for making the 
make_cache_entry() function work on a specific index.


Also, be sure to certify your work by adding your "Signed-off-by: " line 
to each commit.  Details at:

https://github.com/git/git/blob/master/Documentation/SubmittingPatches


> index, instead of implicitly using the_index. This is in preparation
> for making the make_cache_entry function work on a specific index.

[PATCH v1 2/5] Add an API creating / discarding cache_entry structs

[Jameson Miller]

Add an API around managing the lifetime of cache_entry structs. Abstracting
memory management details behind an API will allow for alternative memory
management strategies without affecting all the call sites.  This commit does
not change how memory is allocated / freed. A later commit in this series will
allocate cache entries from memory pools as appropriate.

Motivation:
It has been observed that the time spent loading an index with a large
number of entries is partly dominated by malloc() calls. This
change is in preparation for using memory pools to reduce the number
of malloc() calls made when loading an index.

This API makes a distinction between cache entries that are intended for use
with a particular to an index and cache entries that are not. This enables us
to use the knowledge about how a cache entry will be used to make informed
decisions about how to handle the corresponding memory.
---
 apply.c                |  26 ++++++------
 blame.c                |   5 +--
 builtin/checkout.c     |   8 ++--
 builtin/difftool.c     |   8 ++--
 builtin/reset.c        |   6 +--
 builtin/update-index.c |  26 ++++++------
 cache.h                |  29 +++++++++++++-
 merge-recursive.c      |   2 +-
 read-cache.c           | 105 +++++++++++++++++++++++++++++++++++--------------
 resolve-undo.c         |   6 ++-
 split-index.c          |   8 ++--
 tree.c                 |   4 +-
 unpack-trees.c         |  27 ++++++++-----
 13 files changed, 166 insertions(+), 94 deletions(-)

diff --git a/apply.c b/apply.c
index 7e5792c996..47903f427b 100644
--- a/apply.c
+++ b/apply.c
@@ -4090,12 +4090,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
+		ce = make_index_cache_entry(&result, patch->old_mode, oid.hash, name, 0, 0);
 		if (!ce)
-			return error(_("make_cache_entry failed for path '%s'"),
+			return error(_("make_index_cache_entry failed for path '%s'"),
 				     name);
 		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
-			free(ce);
+			index_cache_entry_discard(ce);
 			return error(_("could not add %s to temporary index"),
 				     name);
 		}
@@ -4263,12 +4263,11 @@ static int add_index_file(struct apply_state *state,
 	struct stat st;
 	struct cache_entry *ce;
 	int namelen = strlen(path);
-	unsigned ce_size = cache_entry_size(namelen);
 
 	if (!state->update_index)
 		return 0;
 
-	ce = xcalloc(1, ce_size);
+	ce = make_empty_index_cache_entry(&the_index, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(0);
@@ -4278,13 +4277,13 @@ static int add_index_file(struct apply_state *state,
 
 		if (!skip_prefix(buf, "Subproject commit ", &s) ||
 		    get_oid_hex(s, &ce->oid)) {
-			free(ce);
-		       return error(_("corrupt patch for submodule %s"), path);
+			index_cache_entry_discard(ce);
+			return error(_("corrupt patch for submodule %s"), path);
 		}
 	} else {
 		if (!state->cached) {
 			if (lstat(path, &st) < 0) {
-				free(ce);
+				index_cache_entry_discard(ce);
 				return error_errno(_("unable to stat newly "
 						     "created file '%s'"),
 						   path);
@@ -4292,13 +4291,13 @@ static int add_index_file(struct apply_state *state,
 			fill_stat_cache_info(ce, &st);
 		}
 		if (write_object_file(buf, size, blob_type, &ce->oid) < 0) {
-			free(ce);
+			index_cache_entry_discard(ce);
 			return error(_("unable to create backing store "
 				       "for newly created file %s"), path);
 		}
 	}
 	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-		free(ce);
+		index_cache_entry_discard(ce);
 		return error(_("unable to add cache entry for %s"), path);
 	}
 
@@ -4422,27 +4421,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
 				       struct patch *patch)
 {
 	int stage, namelen;
-	unsigned ce_size, mode;
+	unsigned mode;
 	struct cache_entry *ce;
 
 	if (!state->update_index)
 		return 0;
 	namelen = strlen(patch->new_name);
-	ce_size = cache_entry_size(namelen);
 	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
 
 	remove_file_from_cache(patch->new_name);
 	for (stage = 1; stage < 4; stage++) {
 		if (is_null_oid(&patch->threeway_stage[stage - 1]))
 			continue;
-		ce = xcalloc(1, ce_size);
+		ce = make_empty_index_cache_entry(&the_index, namelen);
 		memcpy(ce->name, patch->new_name, namelen);
 		ce->ce_mode = create_ce_mode(mode);
 		ce->ce_flags = create_ce_flags(stage);
 		ce->ce_namelen = namelen;
 		oidcpy(&ce->oid, &patch->threeway_stage[stage - 1]);
 		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-			free(ce);
+			index_cache_entry_discard(ce);
 			return error(_("unable to add cache entry for %s"),
 				     patch->new_name);
 		}
diff --git a/blame.c b/blame.c
index 78c9808bd1..8067e398a1 100644
--- a/blame.c
+++ b/blame.c
@@ -154,7 +154,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
 	time_t now;
-	int size, len;
+	int len;
 	struct cache_entry *ce;
 	unsigned mode;
 	struct strbuf msg = STRBUF_INIT;
@@ -252,8 +252,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 			/* Let's not bother reading from HEAD tree */
 			mode = S_IFREG | 0644;
 	}
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, &origin->blob_oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index b49b582071..2ae2aff81a 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -77,7 +77,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_index_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -96,7 +96,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		if (ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			index_cache_entry_discard(ce);
 			return 0;
 		}
 	}
@@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_transient_cache_entry(mode, oid.hash, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	transient_cache_entry_discard(ce);
 	return status;
 }
 
diff --git a/builtin/difftool.c b/builtin/difftool.c
index ee8dce019e..db7b256a7b 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,10 +321,10 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ce = make_transient_cache_entry(mode, oid->hash, path, 0);
 	ret = checkout_entry(ce, state, NULL);
 
-	free(ce);
+	transient_cache_entry_discard(ce);
 	return ret;
 }
 
@@ -488,8 +488,8 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
-							 dst_path, 0, 0);
+					make_index_cache_entry(&wtindex, rmode, roid.hash,
+							       dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
 						ADD_CACHE_JUST_APPEND);
diff --git a/builtin/reset.c b/builtin/reset.c
index 7f1c3f02a3..1062dab73f 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,10 +134,10 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, one->oid.hash, one->path,
-				      0, 0);
+		ce = make_index_cache_entry(&the_index, one->mode, one->oid.hash, one->path,
+					    0, 0);
 		if (!ce)
-			die(_("make_cache_entry failed for path '%s'"),
+			die(_("make_index_cache_entry failed for path '%s'"),
 			    one->path);
 		if (is_missing) {
 			ce->ce_flags |= CE_INTENT_TO_ADD;
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 10d070a76f..9adb366d6c 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -268,15 +268,14 @@ static int process_lstat_error(const char *path, int err)
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
-	int option, size;
+	int option;
 	struct cache_entry *ce;
 
 	/* Was the old index entry already up-to-date? */
 	if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
 		return 0;
 
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
@@ -285,13 +284,13 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 
 	if (index_path(&ce->oid, path, st,
 		       info_only ? 0 : HASH_WRITE_OBJECT)) {
-		free(ce);
+		index_cache_entry_discard(ce);
 		return -1;
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
 	if (add_cache_entry(ce, option)) {
-		free(ce);
+		index_cache_entry_discard(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
 	}
 	return 0;
@@ -403,15 +402,14 @@ static int process_path(const char *path)
 static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 			 const char *path, int stage)
 {
-	int size, len, option;
+	int len, option;
 	struct cache_entry *ce;
 
 	if (!verify_path(path))
 		return error("Invalid path '%s'", path);
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -589,7 +587,6 @@ static struct cache_entry *read_one_ent(const char *which,
 {
 	unsigned mode;
 	struct object_id oid;
-	int size;
 	struct cache_entry *ce;
 
 	if (get_tree_entry(ent, path, &oid, &mode)) {
@@ -602,8 +599,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, namelen);
 
 	oidcpy(&ce->oid, &oid);
 	memcpy(ce->name, path, namelen);
@@ -680,8 +676,8 @@ static int unresolve_one(const char *path)
 	error("%s: cannot add their version to the index.", path);
 	ret = -1;
  free_return:
-	free(ce_2);
-	free(ce_3);
+	index_cache_entry_discard(ce_2);
+	index_cache_entry_discard(ce_3);
 	return ret;
 }
 
@@ -748,7 +744,7 @@ static int do_reupdate(int ac, const char **av,
 					   ce->name, ce_namelen(ce), 0);
 		if (old && ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
-			free(old);
+			index_cache_entry_discard(old);
 			continue; /* unchanged */
 		}
 		/* Be careful.  The working tree may not have the
@@ -759,7 +755,7 @@ static int do_reupdate(int ac, const char **av,
 		path = xstrdup(ce->name);
 		update_one(path);
 		free(path);
-		free(old);
+		index_cache_entry_discard(old);
 		if (save_nr != active_nr)
 			goto redo;
 	}
diff --git a/cache.h b/cache.h
index e50a847aea..eedf154815 100644
--- a/cache.h
+++ b/cache.h
@@ -339,6 +339,34 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 extern void free_name_hash(struct index_state *istate);
 
 
+/* Cache entry creation and freeing */
+
+/*
+ * Create cache_entry intended for use in the specified index. Caller
+ * is responsible for discarding the cache_entry with
+ * `index_cache_entry_discard`.
+ */
+extern struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
+extern struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t name_len);
+
+/*
+ * Create a cache_entry that is not intended to be added to an index.
+ * Caller is responsible for discarding the cache_entry
+ * with `transient_cache_entry_discard`.
+ */
+extern struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage);
+extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
+
+/*
+ * Discard cache entry allocated via `make_*_index_cache_entry`.
+ */
+void index_cache_entry_discard(struct cache_entry *ce);
+
+/*
+ * Discard cache entry allocated via `make_*_transient_cache_entry`.
+ */
+void transient_cache_entry_discard(struct cache_entry *ce);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
@@ -690,7 +718,6 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 693f60e0a3..be118c0c6d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -252,7 +252,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid->hash : null_sha1, path, stage, 0);
+	ce = make_index_cache_entry(&the_index, mode, oid ? oid->hash : null_sha1, path, stage, 0);
 	if (!ce)
 		return err(o, _("addinfo_cache failed for path '%s'"), path);
 
diff --git a/read-cache.c b/read-cache.c
index 2cb4f53b57..04fa7e1bd0 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -61,7 +61,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 	replace_index_entry_in_base(istate, old, ce);
 	remove_name_hash(istate, old);
-	free(old);
+	index_cache_entry_discard(old);
 	ce->ce_flags &= ~CE_HASHED;
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +74,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new_entry = xmalloc(cache_entry_size(namelen));
+	new_entry = make_empty_index_cache_entry(istate, namelen);
 	copy_cache_entry(new_entry, old_entry);
 	new_entry->ce_flags &= ~CE_HASHED;
 	new_entry->ce_namelen = namelen;
@@ -623,7 +623,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new_entry = xcalloc(1, cache_entry_size(len));
+	new_entry = make_empty_index_cache_entry(istate, len);
 	memcpy(new_entry->name, alias->name, len);
 	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
@@ -640,7 +640,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-	int size, namelen, was_same;
+	int namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
@@ -662,8 +662,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_namelen = namelen;
 	if (!intent_only)
@@ -704,13 +703,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 				ce_mark_uptodate(alias);
 			alias->ce_flags |= CE_ADDED;
 
-			free(ce);
+			index_cache_entry_discard(ce);
 			return 0;
 		}
 	}
 	if (!intent_only) {
 		if (index_path(&ce->oid, path, st, newflags)) {
-			free(ce);
+			index_cache_entry_discard(ce);
 			return error("unable to index file %s", path);
 		}
 	} else
@@ -727,9 +726,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		    ce->ce_mode == alias->ce_mode);
 
 	if (pretend)
-		free(ce);
+		index_cache_entry_discard(ce);
 	else if (add_index_entry(istate, ce, add_option)) {
-		free(ce);
+		index_cache_entry_discard(ce);
 		return error("unable to add %s to index", path);
 	}
 	if (verbose && !was_same)
@@ -745,12 +744,22 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 	return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
-		const unsigned char *sha1, const char *path, int stage,
-		unsigned int refresh_options)
+struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_empty_transient_cache_entry(size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode,
+			    const unsigned char *sha1, const char *path,
+			    int stage, unsigned int refresh_options)
 {
-	int size, len;
 	struct cache_entry *ce, *ret;
+	int len;
 
 	if (!verify_path(path)) {
 		error("Invalid path '%s'", path);
@@ -758,8 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	}
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, len);
 
 	hashcpy(ce->oid.hash, sha1);
 	memcpy(ce->name, path, len);
@@ -769,10 +777,34 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 
 	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
-		free(ce);
+		index_cache_entry_discard(ce);
+
 	return ret;
 }
 
+struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1,
+			   const char *path, int stage)
+{
+	struct cache_entry *ce;
+	int len;
+
+	if (!verify_path(path)) {
+		error("Invalid path '%s'", path);
+		return NULL;
+	}
+
+	len = strlen(path);
+	ce = make_empty_transient_cache_entry(len);
+
+	hashcpy(ce->oid.hash, sha1);
+	memcpy(ce->name, path, len);
+	ce->ce_flags = create_ce_flags(stage);
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	return ce;
+}
+
 /*
  * Chmod an index entry with either +x or -x.
  *
@@ -1243,7 +1275,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
 	struct stat st;
 	struct cache_entry *updated;
-	int changed, size;
+	int changed;
 	int refresh = options & CE_MATCH_REFRESH;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
@@ -1323,8 +1355,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
-	size = ce_size(ce);
-	updated = xmalloc(size);
+	updated = make_empty_index_cache_entry(istate, ce_namelen(ce));
 	copy_cache_entry(updated, ce);
 	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
 	fill_stat_cache_info(updated, &st);
@@ -1610,12 +1641,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = xmalloc(cache_entry_size(len));
+	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1657,7 +1689,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *create_from_disk(struct index_state *istate,
+					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
 {
@@ -1688,13 +1721,13 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(ondisk, flags,
+		ce = cache_entry_from_ondisk(istate, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1826,7 +1859,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1932,7 +1965,7 @@ int discard_index(struct index_state *istate)
 		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
 		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
 			continue;
-		free(istate->cache[i]);
+		index_cache_entry_discard(istate->cache[i]);
 	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2622,14 +2655,13 @@ int read_index_unmerged(struct index_state *istate)
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i];
 		struct cache_entry *new_ce;
-		int size, len;
+		int len;
 
 		if (!ce_stage(ce))
 			continue;
 		unmerged = 1;
 		len = ce_namelen(ce);
-		size = cache_entry_size(len);
-		new_ce = xcalloc(1, size);
+		new_ce = make_empty_index_cache_entry(istate, len);
 		memcpy(new_ce->name, ce->name, len);
 		new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
 		new_ce->ce_namelen = len;
@@ -2738,3 +2770,16 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	dst->untracked = src->untracked;
 	src->untracked = NULL;
 }
+
+/*
+ * Free cache entry allocated for an index.
+ */
+void index_cache_entry_discard(struct cache_entry *ce)
+{
+	free(ce);
+}
+
+void transient_cache_entry_discard(struct cache_entry *ce)
+{
+	free(ce);
+}
diff --git a/resolve-undo.c b/resolve-undo.c
index aed95b4b35..96ef6307a6 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,8 +146,10 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], ru->oid[i].hash,
-				       name, i + 1, 0);
+		nce = make_index_cache_entry(istate,
+					     ru->mode[i],
+					     ru->oid[i].hash,
+					     name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
 		if (add_index_entry(istate, nce, ADD_CACHE_OK_TO_ADD)) {
diff --git a/split-index.c b/split-index.c
index 3eb8ff1b43..361c821096 100644
--- a/split-index.c
+++ b/split-index.c
@@ -123,7 +123,7 @@ static void replace_entry(size_t pos, void *data)
 	src->ce_flags |= CE_UPDATE_IN_BASE;
 	src->ce_namelen = dst->ce_namelen;
 	copy_cache_entry(dst, src);
-	free(src);
+	index_cache_entry_discard(src);
 	si->nr_replacements++;
 }
 
@@ -224,7 +224,7 @@ void prepare_to_write_split_index(struct index_state *istate)
 			base->ce_flags = base_flags;
 			if (ret)
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
-			free(base);
+			index_cache_entry_discard(base);
 			si->base->cache[ce->index - 1] = ce;
 		}
 		for (i = 0; i < si->base->cache_nr; i++) {
@@ -301,7 +301,7 @@ void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce
 	    ce == istate->split_index->base->cache[ce->index - 1])
 		ce->ce_flags |= CE_REMOVE;
 	else
-		free(ce);
+		index_cache_entry_discard(ce);
 }
 
 void replace_index_entry_in_base(struct index_state *istate,
@@ -314,7 +314,7 @@ void replace_index_entry_in_base(struct index_state *istate,
 	    old_entry->index <= istate->split_index->base->cache_nr) {
 		new_entry->index = old_entry->index;
 		if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
-			free(istate->split_index->base->cache[new_entry->index - 1]);
+			index_cache_entry_discard(istate->split_index->base->cache[new_entry->index - 1]);
 		istate->split_index->base->cache[new_entry->index - 1] = new_entry;
 	}
 }
diff --git a/tree.c b/tree.c
index 1c68ea586b..1ba39c9374 100644
--- a/tree.c
+++ b/tree.c
@@ -16,15 +16,13 @@ static int read_one_entry_opt(struct index_state *istate,
 			      unsigned mode, int stage, int opt)
 {
 	int len;
-	unsigned int size;
 	struct cache_entry *ce;
 
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 
 	len = strlen(pathname);
-	size = cache_entry_size(baselen + len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, baselen + len);
 
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(stage);
diff --git a/unpack-trees.c b/unpack-trees.c
index e73745051e..232cdecc72 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -192,10 +192,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce)
+static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
 {
 	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = xmalloc(size);
+	struct cache_entry *new_entry = make_empty_index_cache_entry(istate, ce_namelen(ce));
 
 	memcpy(new_entry, ce, size);
 	return new_entry;
@@ -205,7 +205,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce), set, clear);
+	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -786,10 +786,17 @@ static int ce_in_traverse_path(const struct cache_entry *ce,
 	return (info->pathlen < ce_namelen(ce));
 }
 
-static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
+static struct cache_entry *create_ce_entry(const struct traverse_info *info,
+	const struct name_entry *n,
+	int stage,
+	struct index_state *istate,
+	int is_transient)
 {
 	int len = traverse_path_len(info, n);
-	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
+	struct cache_entry *ce =
+		is_transient ?
+		make_empty_transient_cache_entry(len) :
+		make_empty_index_cache_entry(istate, len);
 
 	ce->ce_mode = create_ce_mode(n->mode);
 	ce->ce_flags = create_ce_flags(stage);
@@ -835,7 +842,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 			stage = 3;
 		else
 			stage = 2;
-		src[i + o->merge] = create_ce_entry(info, names + i, stage);
+		src[i + o->merge] = create_ce_entry(info, names + i, stage, &o->result, o->merge);
 	}
 
 	if (o->merge) {
@@ -844,7 +851,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		for (i = 0; i < n; i++) {
 			struct cache_entry *ce = src[i + o->merge];
 			if (ce != o->df_conflict_entry)
-				free(ce);
+				transient_cache_entry_discard(ce);
 		}
 		return rc;
 	}
@@ -1765,7 +1772,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce);
+	struct cache_entry *merge = dup_entry(ce, &o->result);
 
 	if (!old) {
 		/*
@@ -1785,7 +1792,7 @@ static int merged_entry(const struct cache_entry *ce,
 
 		if (verify_absent(merge,
 				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
-			free(merge);
+			index_cache_entry_discard(merge);
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
@@ -1811,7 +1818,7 @@ static int merged_entry(const struct cache_entry *ce,
 			update = 0;
 		} else {
 			if (verify_uptodate(old, o)) {
-				free(merge);
+				index_cache_entry_discard(merge);
 				return -1;
 			}
 			/* Migrate old flags over */
-- 
2.14.3

Re: [PATCH v1 2/5] Add an API creating / discarding cache_entry structs

[Ben Peart]

On 4/17/2018 12:34 PM, Jameson Miller wrote:
> Add an API around managing the lifetime of cache_entry structs. Abstracting
> memory management details behind an API will allow for alternative memory
> management strategies without affecting all the call sites.  This commit does
> not change how memory is allocated / freed. A later commit in this series will
> allocate cache entries from memory pools as appropriate.
> 
> Motivation:
> It has been observed that the time spent loading an index with a large
> number of entries is partly dominated by malloc() calls. This
> change is in preparation for using memory pools to reduce the number
> of malloc() calls made when loading an index.
> 
> This API makes a distinction between cache entries that are intended for use
> with a particular to an index and cache entries that are not. 

The wording here is awkward.  Did you mean "intended for use with a 
particular index?"

This enables us
> to use the knowledge about how a cache entry will be used to make informed
> decisions about how to handle the corresponding memory.
> ---
>   apply.c                |  26 ++++++------
>   blame.c                |   5 +--
>   builtin/checkout.c     |   8 ++--
>   builtin/difftool.c     |   8 ++--
>   builtin/reset.c        |   6 +--
>   builtin/update-index.c |  26 ++++++------
>   cache.h                |  29 +++++++++++++-
>   merge-recursive.c      |   2 +-
>   read-cache.c           | 105 +++++++++++++++++++++++++++++++++++--------------
>   resolve-undo.c         |   6 ++-
>   split-index.c          |   8 ++--
>   tree.c                 |   4 +-
>   unpack-trees.c         |  27 ++++++++-----
>   13 files changed, 166 insertions(+), 94 deletions(-)
> 
> diff --git a/apply.c b/apply.c
> index 7e5792c996..47903f427b 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -4090,12 +4090,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
>   			return error(_("sha1 information is lacking or useless "
>   				       "(%s)."), name);
>   
> -		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
> +		ce = make_index_cache_entry(&result, patch->old_mode, oid.hash, name, 0, 0);
>   		if (!ce)
> -			return error(_("make_cache_entry failed for path '%s'"),
> +			return error(_("make_index_cache_entry failed for path '%s'"),
>   				     name);
>   		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
> -			free(ce);
> +			index_cache_entry_discard(ce);

I personally prefer name symmetry.  To me, make_index_cache_entry() 
should be paired with discard_index_cache_entry().

The rest of this patch looks like a fairly mechanical refactoring with 
the biggest exception being the difference between the the 
*_index_cache_entry() APIs and the *_transient_cache_entry() APIs.

There are quite a few changes but I didn't see any instances that were 
missed or any errors.  I see that later patches will put verification 
code in place to detect if any were done incorrectly and to prevent 
regressions moving forward.

Overall, it looks correct and reasonable.

<snip>

>   
> -struct cache_entry *make_cache_entry(unsigned int mode,
> -		const unsigned char *sha1, const char *path, int stage,
> -		unsigned int refresh_options)
> +struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
> +{
> +	return xcalloc(1, cache_entry_size(len));
> +}
> +
> +struct cache_entry *make_empty_transient_cache_entry(size_t len)
> +{
> +	return xcalloc(1, cache_entry_size(len));
> +}
> +
> +struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode,
> +			    const unsigned char *sha1, const char *path,
> +			    int stage, unsigned int refresh_options)
>   {
> -	int size, len;
>   	struct cache_entry *ce, *ret;
> +	int len;
>   
>   	if (!verify_path(path)) {
>   		error("Invalid path '%s'", path);
> @@ -758,8 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
>   	}
>   
>   	len = strlen(path);
> -	size = cache_entry_size(len);
> -	ce = xcalloc(1, size);
> +	ce = make_empty_index_cache_entry(istate, len);
>   
>   	hashcpy(ce->oid.hash, sha1);
>   	memcpy(ce->name, path, len);
> @@ -769,10 +777,34 @@ struct cache_entry *make_cache_entry(unsigned int mode,
>   
>   	ret = refresh_cache_entry(&the_index, ce, refresh_options);
>   	if (ret != ce)
> -		free(ce);
> +		index_cache_entry_discard(ce);
> +
>   	return ret;
>   }
>   
> +struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1,
> +			   const char *path, int stage)
> +{
> +	struct cache_entry *ce;
> +	int len;
> +
> +	if (!verify_path(path)) {
> +		error("Invalid path '%s'", path);
> +		return NULL;
> +	}
> +
> +	len = strlen(path);
> +	ce = make_empty_transient_cache_entry(len);
> +
> +	hashcpy(ce->oid.hash, sha1);
> +	memcpy(ce->name, path, len);
> +	ce->ce_flags = create_ce_flags(stage);
> +	ce->ce_namelen = len;
> +	ce->ce_mode = create_ce_mode(mode);
> +

Nit, feel free to ignore. There isn't a lot of initialization here but I 
wonder if it makes sense to have an internal helper function to ensure 
these stay the same.

> +	return ce;
> +}
> +
>   /*
>    * Chmod an index entry with either +x or -x.
>    *
> @@ -1243,7 +1275,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
>   {
>   	struct stat st;
>   	struct cache_entry *updated;
> -	int changed, size;
> +	int changed;
>   	int refresh = options & CE_MATCH_REFRESH;
>   	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
>   	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
> @@ -1323,8 +1355,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
>   		return NULL;
>   	}
>   
> -	size = ce_size(ce);
> -	updated = xmalloc(size);
> +	updated = make_empty_index_cache_entry(istate, ce_namelen(ce));
>   	copy_cache_entry(updated, ce);
>   	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
>   	fill_stat_cache_info(updated, &st);
> @@ -1610,12 +1641,13 @@ int read_index(struct index_state *istate)
>   	return read_index_from(istate, get_index_file(), get_git_dir());
>   }
>   
> -static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
> +static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
> +						   struct ondisk_cache_entry *ondisk,
>   						   unsigned int flags,
>   						   const char *name,
>   						   size_t len)
>   {
> -	struct cache_entry *ce = xmalloc(cache_entry_size(len));
> +	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
>   
>   	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
>   	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
> @@ -1657,7 +1689,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
>   	return (const char *)ep + 1 - cp_;
>   }
>   
> -static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
> +static struct cache_entry *create_from_disk(struct index_state *istate,
> +					    struct ondisk_cache_entry *ondisk,
>   					    unsigned long *ent_size,
>   					    struct strbuf *previous_name)

Nit. Just wondering why you pulled refresh_cache_entry() out into an 
earlier/separate commit but then did create_from_disk() as part of the 
large refactoring focused on adding the create/discard APIs?

<snip>

> diff --git a/unpack-trees.c b/unpack-trees.c
> index e73745051e..232cdecc72 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -192,10 +192,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
>   			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
>   }
>   
> -static struct cache_entry *dup_entry(const struct cache_entry *ce)
> +static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)

Ditto with the dup_entry() and create_ce_entry() functions refactoring.

> -static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
> +static struct cache_entry *create_ce_entry(const struct traverse_info *info,
> +	const struct name_entry *n,
> +	int stage,
> +	struct index_state *istate,
> +	int is_transient)

[PATCH v1 4/5] Allocate cache entries from memory pools

[Jameson Miller]

Improve performance of reading a large index by reducing the number of
malloc() calls. When reading an index with a large number of entries,
a portion of the time is dominated in malloc() calls. This can be
mitigated by allocating a single large block of memory up front into a
memory pool and have git hand out chunks of time.

This change moves the cache entry allocation to be on top of memory
pools.

Design:

The index_state struct will gain a notion of an associated memory_pool
from which cache_entry structs will be allocated from. When reading in
the index from disk, we have information on the number of entries and
their size, which can guide us in deciding how large our initial
memory allocation should be. When an index is discarded, the
associated memory_pool and cache entries from the memory pool will be
discarded as well. This means the lifetime of cache_entry structs are
tied to the lifetime of the index_state they were allocated for.

In the case of a Split Index, the following rules are followed. 1st,
some terminology is defined:

Terminology:
  - 'the_index': represents the logical view of the index

  - 'split_index': represents the "base" cache entries. Read from the
    split index file.

'the_index' can reference a single split_index, as well as
cache_entries from the split_index. `the_index` will be discarded
before the `split_index` is.  This means that when we are allocating
cache_entries in the presence of a split index, we need to allocate
the entries from the `split_index`'s memory pool. This allows us to
follow the pattern that `the_index` can reference cache_entries from
the `split_index`, and that the cache_entries will not be freed while
they are still being referenced.
---
 cache.h       |  2 ++
 read-cache.c  | 95 +++++++++++++++++++++++++++++++++++++++++++++--------------
 split-index.c | 23 +++++++++++++--
 3 files changed, 95 insertions(+), 25 deletions(-)

diff --git a/cache.h b/cache.h
index eedf154815..7c0d2343c3 100644
--- a/cache.h
+++ b/cache.h
@@ -15,6 +15,7 @@
 #include "path.h"
 #include "sha1-array.h"
 #include "repository.h"
+#include "mem-pool.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -328,6 +329,7 @@ struct index_state {
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
+	struct mem_pool *ce_mem_pool;
 };
 
 extern struct index_state the_index;
diff --git a/read-cache.c b/read-cache.c
index 04fa7e1bd0..67438bf375 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -46,6 +46,42 @@
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
 		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
+
+/*
+ * This is an estimate of the average pathname length in the index.  We use
+ * this for V4 index files to guess the un-deltafied size of the index in
+ * memory because of pathname deltafication.  This is not required for V2/V3
+ * index formats because their pathnames are not compressed.  If the initial
+ * amount of memory set aside is not sufficient, the mem pool will allocate
+ * extra memory.
+ */
+#define CACHE_ENTRY_AVG_PATH_LENGTH_ESTIMATE 80
+
+static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	return mem_pool_alloc(mem_pool, cache_entry_size(len));
+}
+
+static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
+{
+	return mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
+}
+
+static struct mem_pool *find_mem_pool(struct index_state *istate)
+{
+	struct mem_pool **pool_ptr;
+
+	if (istate->split_index && istate->split_index->base)
+		pool_ptr = &istate->split_index->base->ce_mem_pool;
+	else
+		pool_ptr = &istate->ce_mem_pool;
+
+	if (!*pool_ptr)
+		mem_pool_init(pool_ptr, 0);
+
+	return *pool_ptr;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -746,7 +782,7 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 
 struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
 {
-	return xcalloc(1, cache_entry_size(len));
+	return mem_pool__ce_calloc(find_mem_pool(istate), len);
 }
 
 struct cache_entry *make_empty_transient_cache_entry(size_t len)
@@ -1641,13 +1677,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+static struct cache_entry *cache_entry_from_ondisk(struct mem_pool *mem_pool,
 						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
+	struct cache_entry *ce = mem_pool__ce_alloc(mem_pool, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1689,7 +1725,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct index_state *istate,
+static struct cache_entry *create_from_disk(struct mem_pool *mem_pool,
 					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
@@ -1721,13 +1757,13 @@ static struct cache_entry *create_from_disk(struct index_state *istate,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags,
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1801,6 +1837,22 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_fsmonitor(istate);
 }
 
+static size_t estimate_cache_size_from_compressed(unsigned int entries)
+{
+	return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_AVG_PATH_LENGTH_ESTIMATE);
+}
+
+static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
+{
+	long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
+
+	/*
+	 * Account for potential alignment differences.
+	 */
+	per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	return ondisk_size + entries * per_entry;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1847,10 +1899,15 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
 	istate->initialized = 1;
 
-	if (istate->version == 4)
+	if (istate->version == 4) {
 		previous_name = &previous_name_buf;
-	else
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size_from_compressed(istate->cache_nr));
+	} else {
 		previous_name = NULL;
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size(mmap_size, istate->cache_nr));
+	}
 
 	src_offset = sizeof(*hdr);
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -1859,7 +1916,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate->ce_mem_pool, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1956,17 +2013,6 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-	int i;
-
-	for (i = 0; i < istate->cache_nr; i++) {
-		if (istate->cache[i]->index &&
-		    istate->split_index &&
-		    istate->split_index->base &&
-		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-			continue;
-		index_cache_entry_discard(istate->cache[i]);
-	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -1980,6 +2026,12 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool);
+		istate->ce_mem_pool = NULL;
+	}
+
 	return 0;
 }
 
@@ -2772,11 +2824,10 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 }
 
 /*
- * Free cache entry allocated for an index.
+ * Indicate that a cache entry is no longer is use
  */
 void index_cache_entry_discard(struct cache_entry *ce)
 {
-	free(ce);
 }
 
 void transient_cache_entry_discard(struct cache_entry *ce)
diff --git a/split-index.c b/split-index.c
index 361c821096..a920c0ad07 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,16 +73,31 @@ void move_cache_to_base_index(struct index_state *istate)
 	int i;
 
 	/*
-	 * do not delete old si->base, its index entries may be shared
-	 * with istate->cache[]. Accept a bit of leaking here because
-	 * this code is only used by short-lived update-index.
+	 * If there was a previous base index, then transfer ownership of allocated
+	 * entries to the parent index.
 	 */
+	if (si->base &&
+		si->base->ce_mem_pool) {
+
+		if (!istate->ce_mem_pool)
+			mem_pool_init(&istate->ce_mem_pool, 0);
+
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+	}
+
 	si->base = xcalloc(1, sizeof(*si->base));
 	si->base->version = istate->version;
 	/* zero timestamp disables racy test in ce_write_index() */
 	si->base->timestamp = istate->timestamp;
 	ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
 	si->base->cache_nr = istate->cache_nr;
+
+	/*
+	 * The mem_pool needs to move with the allocated entries.
+	 */
+	si->base->ce_mem_pool = istate->ce_mem_pool;
+	istate->ce_mem_pool = NULL;
+
 	COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
 	mark_base_index_entries(si->base);
 	for (i = 0; i < si->base->cache_nr; i++)
@@ -330,6 +345,8 @@ void add_split_index(struct index_state *istate)
 void remove_split_index(struct index_state *istate)
 {
 	if (istate->split_index) {
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+
 		/*
 		 * can't discard_split_index(&the_index); because that
 		 * will destroy split_index->base->cache[], which may
-- 
2.14.3

[PATCH v1 3/5] mem-pool: fill out functionality

[Jameson Miller]

Adds the following functionality to memory pools:

 - Lifecycle management functions (init, discard)

 - Test whether a memory location is part of the managed pool

 - Function to combine 2 pools

This also adds logic to track all memory allocations made by a memory
pool.

These functions will be used in a future commit in this commit series.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 mem-pool.h |  32 +++++++++++++++++++
 2 files changed, 131 insertions(+), 4 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index 389d7af447..09fb78d093 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -5,6 +5,8 @@
 #include "cache.h"
 #include "mem-pool.h"
 
+#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
+
 static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
 {
 	struct mp_block *p;
@@ -19,6 +21,59 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 	return p;
 }
 
+static void *mem_pool_alloc_custom(struct mem_pool *mem_pool, size_t block_alloc)
+{
+	char *p;
+	ALLOC_GROW(mem_pool->custom, mem_pool->nr + 1, mem_pool->alloc);
+	ALLOC_GROW(mem_pool->custom_end, mem_pool->nr_end + 1, mem_pool->alloc_end);
+
+	p = xmalloc(block_alloc);
+	mem_pool->custom[mem_pool->nr++] = p;
+	mem_pool->custom_end[mem_pool->nr_end++] = p + block_alloc;
+
+	mem_pool->pool_alloc += block_alloc;
+
+	return mem_pool->custom[mem_pool->nr - 1];
+}
+
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
+{
+	if (!(*mem_pool))
+	{
+		*mem_pool = xmalloc(sizeof(struct mem_pool));
+		(*mem_pool)->pool_alloc = 0;
+		(*mem_pool)->mp_block = NULL;
+		(*mem_pool)->block_alloc = BLOCK_GROWTH_SIZE;
+		(*mem_pool)->custom = NULL;
+		(*mem_pool)->nr = 0;
+		(*mem_pool)->alloc = 0;
+		(*mem_pool)->custom_end = NULL;
+		(*mem_pool)->nr_end = 0;
+		(*mem_pool)->alloc_end = 0;
+
+		if (initial_size > 0)
+			mem_pool_alloc_block(*mem_pool, initial_size);
+	}
+}
+
+void mem_pool_discard(struct mem_pool *mem_pool)
+{
+	int i;
+	struct mp_block *block, *block_to_free;
+	for (block = mem_pool->mp_block; block;) {
+		block_to_free = block;
+		block = block->next_block;
+		free(block_to_free);
+	}
+
+	for (i = 0; i < mem_pool->nr; i++)
+		free(mem_pool->custom[i]);
+
+	free(mem_pool->custom);
+	free(mem_pool->custom_end);
+	free(mem_pool);
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p;
@@ -33,10 +88,8 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 			break;
 
 	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2)) {
-			mem_pool->pool_alloc += len;
-			return xmalloc(len);
-		}
+		if (len >= (mem_pool->block_alloc / 2))
+			return mem_pool_alloc_custom(mem_pool, len);
 
 		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
 	}
@@ -53,3 +106,45 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	memset(r, 0, len);
 	return r;
 }
+
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
+{
+	struct mp_block *p;
+	for (p = mem_pool->mp_block; p; p = p->next_block)
+		if ((mem >= ((void *)p->space)) &&
+		    (mem < ((void *)p->end)))
+			return 1;
+
+	return 0;
+}
+
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
+{
+	int i;
+	struct mp_block **tail = &dst->mp_block;
+
+	/* Find pointer of dst's last block (if any) */
+	while (*tail)
+		tail = &(*tail)->next_block;
+
+	/* Append the blocks from src to dst */
+	*tail = src->mp_block;
+
+	ALLOC_GROW(dst->custom, dst->nr + src->nr, dst->alloc);
+	ALLOC_GROW(dst->custom_end, dst->nr_end + src->nr_end, dst->alloc_end);
+
+	for (i = 0; i < src->nr; i++) {
+		dst->custom[dst->nr++] = src->custom[i];
+		dst->custom_end[dst->nr_end++] = src->custom_end[i];
+	}
+
+	dst->pool_alloc += src->pool_alloc;
+	src->pool_alloc = 0;
+	src->mp_block = NULL;
+	src->custom = NULL;
+	src->nr = 0;
+	src->alloc = 0;
+	src->custom_end = NULL;
+	src->nr_end = 0;
+	src->alloc_end = 0;
+}
diff --git a/mem-pool.h b/mem-pool.h
index 829ad58ecf..34df4fa709 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -19,8 +19,27 @@ struct mem_pool {
 
 	/* The total amount of memory allocated by the pool. */
 	size_t pool_alloc;
+
+	/*
+	 * Array of pointers to "custom size" memory allocations.
+	 * This is used for "large" memory allocations.
+	 * The *_end variables are used to track the range of memory
+	 * allocated.
+	 */
+	void **custom, **custom_end;
+	int nr, nr_end, alloc, alloc_end;
 };
 
+/*
+ * Initialize mem_pool specified initial.
+ */
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
+
+/*
+ * Discard a memory pool and free all the memory it is responsible for.
+ */
+void mem_pool_discard(struct mem_pool *mem_pool);
+
 /*
  * Alloc memory from the mem_pool.
  */
@@ -31,4 +50,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
+ * pool will be empty and not contain any memory. It still needs to be free'd
+ * with a call to `mem_pool_discard`.
+ */
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
+
+/*
+ * Check if a memory pointed at by 'mem' is part of the range of
+ * memory managed by the specified mem_pool.
+ */
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
+
 #endif
-- 
2.14.3

Re: [PATCH v1 3/5] mem-pool: fill out functionality

[Jonathan Tan]

On Tue, 17 Apr 2018 16:34:42 +0000
Jameson Miller <jamill@microsoft.com> wrote:

> @@ -19,8 +19,27 @@ struct mem_pool {
>  
>  	/* The total amount of memory allocated by the pool. */
>  	size_t pool_alloc;
> +
> +	/*
> +	 * Array of pointers to "custom size" memory allocations.
> +	 * This is used for "large" memory allocations.
> +	 * The *_end variables are used to track the range of memory
> +	 * allocated.
> +	 */
> +	void **custom, **custom_end;
> +	int nr, nr_end, alloc, alloc_end;

This seems overly complicated - the struct mem_pool already has a linked
list of pages, so couldn't you create a custom page and insert it behind
the current front page instead whenever you needed a large-size page?

Also, when combining, there could be some wasted space on one of the
pages. I'm not sure if that's worth calling out, though.

Re: [PATCH v1 3/5] mem-pool: fill out functionality

[Jameson Miller]

On 04/20/2018 07:21 PM, Jonathan Tan wrote:
> On Tue, 17 Apr 2018 16:34:42 +0000
> Jameson Miller <jamill@microsoft.com> wrote:
> 
>> @@ -19,8 +19,27 @@ struct mem_pool {
>>   
>>   	/* The total amount of memory allocated by the pool. */
>>   	size_t pool_alloc;
>> +
>> +	/*
>> +	 * Array of pointers to "custom size" memory allocations.
>> +	 * This is used for "large" memory allocations.
>> +	 * The *_end variables are used to track the range of memory
>> +	 * allocated.
>> +	 */
>> +	void **custom, **custom_end;
>> +	int nr, nr_end, alloc, alloc_end;
> 
> This seems overly complicated - the struct mem_pool already has a linked
> list of pages, so couldn't you create a custom page and insert it behind
> the current front page instead whenever you needed a large-size page?

Yes - that is another option. However, the linked list of pages includes 
memory that *could* have space for an allocation, while the "custom" 
region will never have left over memory that can be used for other 
allocations. When searching pages for memory to satisfy a request, there 
is no reason to search through the "custom" pages. There is a trade-off 
between complexity and implementation, so I am open to suggestions.

This was discussed in [1], where it originally was implemented closer to 
what you describe here.

> 
> Also, when combining, there could be some wasted space on one of the
> pages. I'm not sure if that's worth calling out, though.
> 

Yes, we bring over the whole page. However, these pages are now 
available for new allocations.

[1]
https://public-inbox.org/git/xmqqk1u2k91l.fsf@gitster-ct.c.googlers.com/

Re: [PATCH v1 3/5] mem-pool: fill out functionality

[Jonathan Tan]

On Mon, 23 Apr 2018 13:27:09 -0400
Jameson Miller <jameson.miller81@gmail.com> wrote:

> > This seems overly complicated - the struct mem_pool already has a linked
> > list of pages, so couldn't you create a custom page and insert it behind
> > the current front page instead whenever you needed a large-size page?
> 
> Yes - that is another option. However, the linked list of pages includes 
> memory that *could* have space for an allocation, while the "custom" 
> region will never have left over memory that can be used for other 
> allocations. When searching pages for memory to satisfy a request, there 
> is no reason to search through the "custom" pages. There is a trade-off 
> between complexity and implementation, so I am open to suggestions.
> 
> This was discussed in [1], where it originally was implemented closer to 
> what you describe here.
> 
> > Also, when combining, there could be some wasted space on one of the
> > pages. I'm not sure if that's worth calling out, though.
> 
> Yes, we bring over the whole page. However, these pages are now 
> available for new allocations.
> 
> [1]
> https://public-inbox.org/git/xmqqk1u2k91l.fsf@gitster-ct.c.googlers.com/

Ah, I didn't realize that the plan was to search over all pages when
allocating memory from the pool, instead of only searching the last
page. This seems like a departure from the fast-import.c way, where as
far as I can tell, new_object() searches only one page. If we do plan to
do this, searching all pages doesn't seem like a good idea to me,
especially since the objects we're storing in the pool are of similar
size.

If we decide to go ahead with searching all the pages, though, the
"custom" pages should probably be another linked list instead of an
array.

Re: [PATCH v1 3/5] mem-pool: fill out functionality

[Jameson Miller]

On 04/23/2018 01:49 PM, Jonathan Tan wrote:
> On Mon, 23 Apr 2018 13:27:09 -0400
> Jameson Miller <jameson.miller81@gmail.com> wrote:
> 
>>> This seems overly complicated - the struct mem_pool already has a linked
>>> list of pages, so couldn't you create a custom page and insert it behind
>>> the current front page instead whenever you needed a large-size page?
>>
>> Yes - that is another option. However, the linked list of pages includes
>> memory that *could* have space for an allocation, while the "custom"
>> region will never have left over memory that can be used for other
>> allocations. When searching pages for memory to satisfy a request, there
>> is no reason to search through the "custom" pages. There is a trade-off
>> between complexity and implementation, so I am open to suggestions.
>>
>> This was discussed in [1], where it originally was implemented closer to
>> what you describe here.
>>
>>> Also, when combining, there could be some wasted space on one of the
>>> pages. I'm not sure if that's worth calling out, though.
>>
>> Yes, we bring over the whole page. However, these pages are now
>> available for new allocations.
>>
>> [1]
>> https://public-inbox.org/git/xmqqk1u2k91l.fsf@gitster-ct.c.googlers.com/
> 
> Ah, I didn't realize that the plan was to search over all pages when
> allocating memory from the pool, instead of only searching the last
> page. This seems like a departure from the fast-import.c way, where as
> far as I can tell, new_object() searches only one page. If we do plan to
> do this, searching all pages doesn't seem like a good idea to me,
> especially since the objects we're storing in the pool are of similar
> size.

I see. However, the new_object() logic in fast-import is a different 
than the logic mem_pool was abstracting, and is not covered by the 
mem_pool functionality. The behavior of searching over all pages for one 
to satisfy the request existed previously and was not changed in the 
mem_pool implementation.

> 
> If we decide to go ahead with searching all the pages, though, the
> "custom" pages should probably be another linked list instead of an
> array.
> 

This is an option - I went with the current design because we only need 
pointers to a block of memory (as well tracking how large the allocation 
is for verification purposes). We don't necessarily need the extra 
overhead of a structure to track the linked list nodes, when it is 
provided by the existing array manipulation functions. I am open to 
feedback on this point, however.

[PATCH v1 5/5] Add optional memory validations around cache_entry lifecyle

[Jameson Miller]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.
---
 cache.h      |  7 +++++++
 git.c        |  3 +++
 mem-pool.c   | 35 ++++++++++++++++++++++++++++++++++-
 mem-pool.h   |  2 ++
 read-cache.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 90 insertions(+), 1 deletion(-)

diff --git a/cache.h b/cache.h
index 7c0d2343c3..f8934d8113 100644
--- a/cache.h
+++ b/cache.h
@@ -369,6 +369,13 @@ void index_cache_entry_discard(struct cache_entry *ce);
  */
 void transient_cache_entry_discard(struct cache_entry *ce);
 
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/git.c b/git.c
index 3a89893712..16b6c1685b 100644
--- a/git.c
+++ b/git.c
@@ -347,7 +347,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index 09fb78d093..a7e28934b0 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -60,20 +60,44 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 {
 	int i;
 	struct mp_block *block, *block_to_free;
+	int invalidate_memory = should_validate_cache_entries();
+
 	for (block = mem_pool->mp_block; block;) {
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
-	for (i = 0; i < mem_pool->nr; i++)
+	for (i = 0; i < mem_pool->nr; i++) {
+		if (invalidate_memory)
+			memset(mem_pool->custom[i], 0xDD, ((char *)mem_pool->custom_end[i]) - ((char *)mem_pool->custom[i]));
+
 		free(mem_pool->custom[i]);
+	}
 
 	free(mem_pool->custom);
 	free(mem_pool->custom_end);
 	free(mem_pool);
 }
 
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p;
@@ -110,11 +134,20 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
 {
 	struct mp_block *p;
+	int i;
+
+	/* Check if memory is allocated in a block */
 	for (p = mem_pool->mp_block; p; p = p->next_block)
 		if ((mem >= ((void *)p->space)) &&
 		    (mem < ((void *)p->end)))
 			return 1;
 
+	/* Check custom memory allocations */
+	for (i = 0; i < mem_pool->nr; i++)
+		if (mem >= mem_pool->custom[i] &&
+		    mem < mem_pool->custom_end[i])
+			return 1;
+
 	return 0;
 }
 
diff --git a/mem-pool.h b/mem-pool.h
index 34df4fa709..b1f9a920ba 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -63,4 +63,6 @@ void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
  */
 int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
 
+int should_validate_cache_entries(void);
+
 #endif
diff --git a/read-cache.c b/read-cache.c
index 67438bf375..d2181a0334 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1290,6 +1290,7 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 			   istate->cache_nr - pos - 1);
 	set_index_entry(istate, pos, ce);
 	istate->cache_changed |= CE_ENTRY_ADDED;
+
 	return 0;
 }
 
@@ -2013,6 +2014,8 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
+	validate_cache_entries(istate);
+
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -2035,6 +2038,43 @@ int discard_index(struct index_state *istate)
 	return 0;
 }
 
+
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+	int validate_index_cache_entries = should_validate_cache_entries();
+
+	if (!validate_index_cache_entries)
+		return;
+
+	if (!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2828,6 +2868,10 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
  */
 void index_cache_entry_discard(struct cache_entry *ce)
 {
+	int invalidate_cache_entry = should_validate_cache_entries();
+
+	if (ce && invalidate_cache_entry)
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
 }
 
 void transient_cache_entry_discard(struct cache_entry *ce)
-- 
2.14.3

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Ben Peart]

On 4/17/2018 12:34 PM, Jameson Miller wrote:

> 100K
> 
> Test                                       baseline [4]       block_allocation
>   ------------------------------------------------------------------------------------
> 0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)    0.02(0.01+0.01) -33.3%
> 
> 1M:
> 
> Test                                       baseline           block_allocation
>   ------------------------------------------------------------------------------------
> 0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)    0.17(0.07+0.09) -26.1%
> 
> 2M:
> 
> Test                                       baseline           block_allocation
>   ------------------------------------------------------------------------------------
> 0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)    0.39(0.17+0.20) -13.3%
> 
> 
> 100K is not a large enough sample size to show the perf impact of this
> change, but we can see a perf improvement with 1M and 2M entries.

I see a 33% change with 100K files which is a substantial improvement 
even in the 100K case.  I do see that the actual wall clock savings 
aren't nearly as much with a small repo as it is with the larger repos 
which makes sense.

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Jameson Miller]

On 04/17/2018 02:39 PM, Ben Peart wrote:
>
>
> On 4/17/2018 12:34 PM, Jameson Miller wrote:
>
>> 100K
>>
>> Test                                       baseline [4] block_allocation
>> ------------------------------------------------------------------------------------
>> 0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01) 
>> 0.02(0.01+0.01) -33.3%
>>
>> 1M:
>>
>> Test                                       baseline block_allocation
>> ------------------------------------------------------------------------------------
>> 0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11) 
>> 0.17(0.07+0.09) -26.1%
>>
>> 2M:
>>
>> Test                                       baseline block_allocation
>> ------------------------------------------------------------------------------------
>> 0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19) 
>> 0.39(0.17+0.20) -13.3%
>>
>>
>> 100K is not a large enough sample size to show the perf impact of this
>> change, but we can see a perf improvement with 1M and 2M entries.
>
> I see a 33% change with 100K files which is a substantial improvement 
> even in the 100K case.  I do see that the actual wall clock savings 
> aren't nearly as much with a small repo as it is with the larger repos 
> which makes sense.

You are correct - I should have been more careful in my wording. What I 
meant is that the wall time savings with 100K is not large, because this 
operation is already very fast.

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> This patch series improves the performance of loading indexes by
> reducing the number of malloc() calls. ...
>
> Jameson Miller (5):
>   read-cache: teach refresh_cache_entry to take istate
>   Add an API creating / discarding cache_entry structs
>   mem-pool: fill out functionality
>   Allocate cache entries from memory pools
>   Add optional memory validations around cache_entry lifecyle
>
>  apply.c                |  26 +++---
>  blame.c                |   5 +-
>  builtin/checkout.c     |   8 +-
>  builtin/difftool.c     |   8 +-
>  builtin/reset.c        |   6 +-
>  builtin/update-index.c |  26 +++---
>  cache.h                |  40 ++++++++-
>  git.c                  |   3 +
>  mem-pool.c             | 136 ++++++++++++++++++++++++++++-
>  mem-pool.h             |  34 ++++++++
>  merge-recursive.c      |   4 +-
>  read-cache.c           | 229 +++++++++++++++++++++++++++++++++++++++----------
>  resolve-undo.c         |   6 +-
>  split-index.c          |  31 +++++--
>  tree.c                 |   4 +-
>  unpack-trees.c         |  27 +++---
>  16 files changed, 476 insertions(+), 117 deletions(-)
>
>
> base-commit: cafaccae98f749ebf33495aec42ea25060de8682

I couldn't quite figure out what these five patches were based on,
even with this line.  Basing on and referring to a commit that is
not part of our published history with "base-commit" is not all that
useful to others.

Offhand without applying these patches and viewing the changes in
wider contexts, one thing that makes me wonder is how the two
allocation schemes can be used with two implementations of free().
Upon add_index_entry() that replaces an index entry for an existing
path, we'd discard an entry that was originally read as part of
read_cache().  If we do that again, the second add_index_entry()
will be discading, in its call to replace_index_entry(), the entry
that was allocated by the caller of the first add_index_entry()
call.  And replace_index_entry() would not have a way to know from
which allocation the entry's memory came from.

Perhaps it is not how you are using the "transient" stuff, and from
the comment in 2/5, it is for "entries that are not meant to go into
the index", but then higher stage index entries in unpack_trees seem
to be allocated via the "transient" stuff, so I am not sure what the
plans are for things like merge_recursive() that uses unpack_trees()
to prepare the index and then later "fix it up" by further futzing
around the index to adjust for renames it finds, etc.

Let me read it fully once we know where these patches are to be
applied, but before that I cannot say much about them X-<.

Thanks.

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Stefan Beller]

>> base-commit: cafaccae98f749ebf33495aec42ea25060de8682
>
> I couldn't quite figure out what these five patches were based on,
> even with this line.  Basing on and referring to a commit that is
> not part of our published history with "base-commit" is not all that
> useful to others.

I'd like to second this. In the object store refactoring, I am at a point where
I'd want to migrate the memory management of {object, tree, commit, tag}.c
which currently is done in alloc.c to a memory pool, that has a dedicated
pointer to it.

So I'd either have to refactor alloc.c to take the_repository[1] or
I'd play around with the mem_pool to manage memory in the
object layer. I guess this playing around can happen with
what is at origin/jm/mem-pool, however the life cycle management
part of the third patch[2] would allow for stopping memleaks there.
So I am interested in this series as well.

[1] proof of concept in patches nearby
https://public-inbox.org/git/20180206001749.218943-31-sbeller@google.com/

[2] https://public-inbox.org/git/20180417163400.3875-5-jamill@microsoft.com/

Thanks,
Stefan

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Jameson Miller]

On 04/20/2018 01:49 PM, Stefan Beller wrote:
>>> base-commit: cafaccae98f749ebf33495aec42ea25060de8682
>>
>> I couldn't quite figure out what these five patches were based on,
>> even with this line.  Basing on and referring to a commit that is
>> not part of our published history with "base-commit" is not all that
>> useful to others.
> 
> I'd like to second this. In the object store refactoring, I am at a point where
> I'd want to migrate the memory management of {object, tree, commit, tag}.c
> which currently is done in alloc.c to a memory pool, that has a dedicated
> pointer to it.
> 
> So I'd either have to refactor alloc.c to take the_repository[1] or
> I'd play around with the mem_pool to manage memory in the
> object layer. I guess this playing around can happen with
> what is at origin/jm/mem-pool, however the life cycle management
> part of the third patch[2] would allow for stopping memleaks there.
> So I am interested in this series as well.
>

Sorry about the confusion here. This patch series can be applied to the 
next branch. They apply cleanly on [3]. The lifecycle functions are 
re-introduced in [4], which we could incorporate sooner if useful. I 
didn't have a consumer for the calls in the original patch series, and 
so deferred them until there was a caller. I would be interested to 
understand how the mem_pool would fit your needs, and if it is 
sufficient or needs modification for your use cases.

> [1] proof of concept in patches nearby
> https://public-inbox.org/git/20180206001749.218943-31-sbeller@google.com/
> 
> [2] https://public-inbox.org/git/20180417163400.3875-5-jamill@microsoft.com/
> 
> Thanks,
> Stefan
> 

[3] b46fe60e1d ("merge-fix/ps/test-chmtime-get", 2018-04-20)

[4]
https://public-inbox.org/git/20180417163400.3875-5-jamill@microsoft.com/

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Stefan Beller]

On Mon, Apr 23, 2018 at 9:44 AM, Jameson Miller
<jameson.miller81@gmail.com> wrote:
> I would be interested to understand how the
> mem_pool would fit your needs, and if it is sufficient or needs modification
> for your use cases.
>
>> [1] proof of concept in patches nearby
>> https://public-inbox.org/git/20180206001749.218943-31-sbeller@google.com/
>>

Currenlty the parsed objects are loaded into memory and never freed.
See alloc.c which implements a specialized memory allocator for this
object loading.
When working with submodules, their objects are also just put into this
globally-namespaced object store. (See struct object **obj_hash in
object.c)

I want to make the object store a per-repository object, such that
when working with submodules, you can free up all submodule objects
once you are done with a given submodule.

To do so, the memory allocation needs to manage the whole life cycle,
while preserving the efficiency of alloc.c. See 855419f764
(Add specialized object allocator, 2006-06-19). The mem-pool that
you propose can allocate large slabs of memory and we can put
objects in there without alignment overhead, such that we preserve
the memory efficiency while being able to track all the memory.

So I would think it is sufficient as-is with this series, maybe we need
a little tweaking there, but nothing large IMHO.

Thanks,
Stefan

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Jameson Miller]

On 04/18/2018 12:49 AM, Junio C Hamano wrote:
> Jameson Miller <jamill@microsoft.com> writes:
>
>> This patch series improves the performance of loading indexes by
>> reducing the number of malloc() calls. ...
>>
>> Jameson Miller (5):
>>    read-cache: teach refresh_cache_entry to take istate
>>    Add an API creating / discarding cache_entry structs
>>    mem-pool: fill out functionality
>>    Allocate cache entries from memory pools
>>    Add optional memory validations around cache_entry lifecyle
>>
>>   apply.c                |  26 +++---
>>   blame.c                |   5 +-
>>   builtin/checkout.c     |   8 +-
>>   builtin/difftool.c     |   8 +-
>>   builtin/reset.c        |   6 +-
>>   builtin/update-index.c |  26 +++---
>>   cache.h                |  40 ++++++++-
>>   git.c                  |   3 +
>>   mem-pool.c             | 136 ++++++++++++++++++++++++++++-
>>   mem-pool.h             |  34 ++++++++
>>   merge-recursive.c      |   4 +-
>>   read-cache.c           | 229 +++++++++++++++++++++++++++++++++++++++----------
>>   resolve-undo.c         |   6 +-
>>   split-index.c          |  31 +++++--
>>   tree.c                 |   4 +-
>>   unpack-trees.c         |  27 +++---
>>   16 files changed, 476 insertions(+), 117 deletions(-)
>>
>>
>> base-commit: cafaccae98f749ebf33495aec42ea25060de8682
> I couldn't quite figure out what these five patches were based on,
> even with this line.  Basing on and referring to a commit that is
> not part of our published history with "base-commit" is not all that
> useful to others.
My apologies - this patch series should be applied to the 'next'
branch.  It applies cleanly on top of
b46fe60e1d ("merge-fix/ps/test-chmtime-get", 2018-04-20), which
is a commit in the 'next' branch.
> Offhand without applying these patches and viewing the changes in
> wider contexts, one thing that makes me wonder is how the two
> allocation schemes can be used with two implementations of free().
> Upon add_index_entry() that replaces an index entry for an existing
> path, we'd discard an entry that was originally read as part of
> read_cache().  If we do that again, the second add_index_entry()
> will be discading, in its call to replace_index_entry(), the entry
> that was allocated by the caller of the first add_index_entry()
> call.  And replace_index_entry() would not have a way to know from
> which allocation the entry's memory came from.
>
> Perhaps it is not how you are using the "transient" stuff, and from
> the comment in 2/5, it is for "entries that are not meant to go into
> the index", but then higher stage index entries in unpack_trees seem
> to be allocated via the "transient" stuff, so I am not sure what the
> plans are for things like merge_recursive() that uses unpack_trees()
> to prepare the index and then later "fix it up" by further futzing
> around the index to adjust for renames it finds, etc.

Good points. The intention with this logic is that any entries
that *could* go into an index are allocated from the memory
pool. The "transient" entries only exist for a short period of
time. These have a defined lifetime and we can always trace the
corresponding "free" call. make_transient_cache_entry() is only
used to construct a temporary cache_entry to pass to the
checkout_entry() / write_entry(). There is a note in checkout.c
indicating that write_entry() needs to be re-factored to not take
a cache_entry.

The cache_entry type could gain knowledge about where it was
allocated from. This would allow us to only have a
single "free()" function, which could inspect the cache_entry to
see if it was allocated from a mem_pool (and possibly which
mem_pool) and take the appropriate action. The downside of this
approach is that cache_entry would need to gain a field to track
this information, and I *think* all of the bit field spots are
taken.

> Let me read it fully once we know where these patches are to be
> applied, but before that I cannot say much about them X-<.
>
> Thanks.
>

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Jonathan Tan]

On Tue, 17 Apr 2018 16:34:39 +0000
Jameson Miller <jamill@microsoft.com> wrote:

> Jameson Miller (5):
>   read-cache: teach refresh_cache_entry to take istate
>   Add an API creating / discarding cache_entry structs
>   mem-pool: fill out functionality
>   Allocate cache entries from memory pools
>   Add optional memory validations around cache_entry lifecyle

In this patch set, there is no enforcement that the cache entry created
by make_index_cache_entry() goes into the correct index when
add_index_entry() is invoked. (Junio described similar things, I
believe, in [1].) This might be an issue when we bring up and drop
multiple indexes, and dropping one index causes a cache entry in another
to become invalidated.

One solution is to store the index for which the cache entry was created
in the cache entry itself, but that does increase its size. Another is
to change the API such that a cache entry is created and added in the
same function, and then have some rollback if the cache entry turns out
to be invalid (to support add-empty-entry -> fill -> verify), but I
don't know if this is feasible. Anyway, all these alternatives should be
at least discussed in the commit message, I think.

The make_transient_cache_entry() function might be poorly named, since
as far as I can tell, the entries produced by that function are actually
the longest lasting, since they are never freed.

Along those lines, I was slightly surprised to find out in patch 4 that
cache entry freeing is a no-op. That's fine, but in that case, it would
be better to delete all the calls to the "discard" function, and
document in the others that the entries they create will only be freed
when the memory pool itself is discarded.

[1] https://public-inbox.org/git/xmqqwox5i0f7.fsf@gitster-ct.c.googlers.com/

Re: [PATCH v1 0/5] Allocate cache entries from memory pool

[Jameson Miller]

On 04/20/2018 07:34 PM, Jonathan Tan wrote:
> On Tue, 17 Apr 2018 16:34:39 +0000
> Jameson Miller <jamill@microsoft.com> wrote:
> 
>> Jameson Miller (5):
>>    read-cache: teach refresh_cache_entry to take istate
>>    Add an API creating / discarding cache_entry structs
>>    mem-pool: fill out functionality
>>    Allocate cache entries from memory pools
>>    Add optional memory validations around cache_entry lifecyle
> 
> In this patch set, there is no enforcement that the cache entry created
> by make_index_cache_entry() goes into the correct index when
> add_index_entry() is invoked. (Junio described similar things, I
> believe, in [1].) This might be an issue when we bring up and drop
> multiple indexes, and dropping one index causes a cache entry in another
> to become invalidated.

Correct - it is up to the caller here to coordinate this. The code 
should be set up so this is not a problem here. In the case of a 
split-index, the cache entries should be allocated from the memory pool 
associated with the "most common" / base index. If you found a place I 
missed or seems questionable, or have suggestions, I would be glad to 
look into it.

> 
> One solution is to store the index for which the cache entry was created
> in the cache entry itself, but that does increase its size. Another is

Yes, this is an option. For this initial patch series, I decided to not 
add extra fields to the cache_entry type, but I think incorporating this 
in cache_entry is a viable option, and has some positive properties.

> to change the API such that a cache entry is created and added in the
> same function, and then have some rollback if the cache entry turns out
> to be invalid (to support add-empty-entry -> fill -> verify), but I
> don't know if this is feasible. Anyway, all these alternatives should be
> at least discussed in the commit message, I think.

I can include a discussion of these in the commit message. Thanks.

> 
> The make_transient_cache_entry() function might be poorly named, since
> as far as I can tell, the entries produced by that function are actually
> the longest lasting, since they are never freed.

They should always be freed (and are usually freed close to where they 
are allocated, or by the calling function). If you see an instance where 
this is not the case, please point it out, because that is not the 
intention.

> 
> Along those lines, I was slightly surprised to find out in patch 4 that
> cache entry freeing is a no-op. That's fine, but in that case, it would
> be better to delete all the calls to the "discard" function, and
> document in the others that the entries they create will only be freed
> when the memory pool itself is discarded.

I can add a comment inside the function body. In the next commit, I do 
add logic to perform extra (optional) verification in the discard 
function. I did wrestle with this fact, but I feel there is value in 
having the locations where it is appropriate to free these entries in 
code, even if this particular implementation is not utilizing it right 
now. Hopefully the verification logic added in 5/5 is enough to justify 
keeping this function around.

> 
> [1] https://public-inbox.org/git/xmqqwox5i0f7.fsf@gitster-ct.c.googlers.com/
> 

[PATCH v2 0/5] Allocate cache entries from memory pool

[Jameson Miller]

Changes from V1:

 - Based patch series off of commit in master

 - Minor updates based on initial code review feedback

Summary:

This patch series improves the performance of loading indexes by
reducing the number of malloc() calls. Loading the index from disk is
partly dominated by the time in malloc(), which is called for each
index entry. This patch series reduces the number of times malloc() is
called as part of loading the index, and instead allocates a block of
memory upfront that is large enough to hold all of the cache entries,
and chunks this memory itself. This change builds on [1].


Git previously allocated block of memory for the index cache entries
until [2].

This 5 part patch series is broken up as follows:

  1/5, 2/5 - Move cache entry lifecycle methods behind an API

  3/5 - Fill out memory pool API to include lifecycle and other
      	methods used in later patches

  4/5 - Allocate cache entry structs from memory pool

  5/5 - Add extra optional validation

Performance Benchmarks:

To evaluate the performance of this approach, the p0002-read-cache.sh
test was run with several combinations of allocators (glibc default,
tcmalloc, jemalloc), with and without block allocation, and across
several different index sized (100K, 1M, 2M entries). The details on
how these repositories were constructed can be found in [3].The
p0002-read-cache.sh was run with the iteration count set to 1 and
$GIT_PERF_REPEAT_COUNT=10.

The tests were run with iteration count set to 1 because this best
approximates the real behavior. The read_cache/discard_cache test will
load / free the index N times, and the performance of this logic is
different between N = 1 and N > 1. As the production code does not
read / discard the index in a loop, a better approximation is when N =
1.

100K

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)    0.02(0.01+0.01) -33.3%

1M:

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)    0.17(0.07+0.09) -26.1%

2M:

Test                                       baseline           block_allocation
 ------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)    0.39(0.17+0.20) -13.3%

With 100K entries, it only takes 0.3 seconds to read the entries even
without using block allocation, so there is only a small change in the
wall clock time. We can see a larger wall clack improvement with 1M
and 2M entries.

For completeness, here is the p0002-read-cache tests for git.git and
linux.git:

git.git:

Test                                          baseline          block_allocation
 ---------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   0.30(0.26+0.03)   0.17(0.13+0.03) -43.3%

linux.git:

Test                                          baseline          block_allocation
 ---------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   7.05(6.01+0.84)   4.61(3.74+0.66) -34.6% 


We also investigated the performance of just using different
allocators. We can see that there is not a consistent performance
gain.

100K

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.03(0.01+0.01)   0.03(0.01+0.01) +0.0%     0.03(0.02+0.01) +0.0% 

1M:

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.23(0.12+0.11)   0.21(0.10+0.10) -8.7%     0.27(0.16+0.10) +17.4%

2M:

Test                                       baseline          tcmalloc                  jemalloc
 ------------------------------------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1 times   0.45(0.26+0.19)   0.46(0.25+0.21) +2.2%     0.57(0.36+0.21) +26.7%



[1] https://public-inbox.org/git/20180321164152.204869-1-jamill@microsoft.com/

[2] debed2a629 (read-cache.c: allocate index entries individually - 2011-10-24)

[3] Constructing test repositories:

The test repositories were constructed with t/perf/repos/many_files.sh with the following parameters:

100K:	 many-files.sh 4 10 9
1M:	 many-files.sh 5 10 9
2M:	 many-files.sh 6 8 7

Base Ref: master
Web-Diff: git@github.com:jamill/git.git/commit/2152d28016
Checkout: git fetch git@github.com:jamill/git.git users/jamill/block_allocation-v2 && git checkout 2152d28016

Jameson Miller (5):
  read-cache: teach refresh_cache_entry() to take istate
  block alloc: add lifecycle APIs for cache_entry structs
  mem-pool: fill out functionality
  block alloc: allocate cache entries from mem_pool
  block alloc: add validations around cache_entry lifecyle

 apply.c                |  26 +++---
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   8 +-
 builtin/reset.c        |   6 +-
 builtin/update-index.c |  26 +++---
 cache.h                |  40 ++++++++-
 git.c                  |   3 +
 mem-pool.c             | 136 ++++++++++++++++++++++++++++-
 mem-pool.h             |  34 ++++++++
 merge-recursive.c      |   4 +-
 read-cache.c           | 232 +++++++++++++++++++++++++++++++++++++++----------
 resolve-undo.c         |   6 +-
 split-index.c          |  31 +++++--
 tree.c                 |   4 +-
 unpack-trees.c         |  27 +++---
 16 files changed, 479 insertions(+), 117 deletions(-)


base-commit: 1f1cddd558b54bb0ce19c8ace353fd07b758510d
-- 
2.14.3

[PATCH v2 1/5] read-cache: teach refresh_cache_entry() to take istate

[Jameson Miller]

Refactor refresh_cache_entry() to work on a specific index, instead of
implicitly using the_index. This is in preparation for making the
make_cache_entry function work on a specific index.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h           | 2 +-
 merge-recursive.c | 2 +-
 read-cache.c      | 7 ++++---
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/cache.h b/cache.h
index 77b7acebb6..31f8f0420a 100644
--- a/cache.h
+++ b/cache.h
@@ -743,7 +743,7 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 #define REFRESH_IGNORE_SUBMODULES	0x0010	/* ignore submodules */
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
-extern struct cache_entry *refresh_cache_entry(struct cache_entry *, unsigned int);
+extern struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 /*
  * Opportunistically update the index but do not complain if we can't.
diff --git a/merge-recursive.c b/merge-recursive.c
index 0c0d48624d..693f60e0a3 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -260,7 +260,7 @@ static int add_cacheinfo(struct merge_options *o,
 	if (refresh) {
 		struct cache_entry *nce;
 
-		nce = refresh_cache_entry(ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		nce = refresh_cache_entry(&the_index, ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
 		if (!nce)
 			return err(o, _("addinfo_cache failed for path '%s'"), path);
 		if (nce != ce)
diff --git a/read-cache.c b/read-cache.c
index 10f1c6bb8a..2cb4f53b57 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -767,7 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	ce->ce_namelen = len;
 	ce->ce_mode = create_ce_mode(mode);
 
-	ret = refresh_cache_entry(ce, refresh_options);
+	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
 		free(ce);
 	return ret;
@@ -1448,10 +1448,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	return has_errors;
 }
 
-struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+					       struct cache_entry *ce,
 					       unsigned int options)
 {
-	return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
-- 
2.14.3

[PATCH v2 2/5] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

Add an API around managing the lifetime of cache_entry
structs. Abstracting memory management details behind an API will
allow for alternative memory management strategies without affecting
all the call sites.  This commit does not change how memory is
allocated / freed. A later commit in this series will allocate cache
entries from memory pools as appropriate.

Motivation:
It has been observed that the time spent loading an index with a large
number of entries is partly dominated by malloc() calls. This change
is in preparation for using memory pools to reduce the number of
malloc() calls made when loading an index.

This API makes a distinction between cache entries that are intended
for use with a particular index and cache entries that are not. This
enables us to use the knowledge about how a cache entry will be used
to make informed decisions about how to handle the corresponding
memory.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 apply.c                |  26 ++++++------
 blame.c                |   5 +--
 builtin/checkout.c     |   8 ++--
 builtin/difftool.c     |   8 ++--
 builtin/reset.c        |   6 +--
 builtin/update-index.c |  26 ++++++------
 cache.h                |  29 +++++++++++++-
 merge-recursive.c      |   2 +-
 read-cache.c           | 105 +++++++++++++++++++++++++++++++++++--------------
 resolve-undo.c         |   6 ++-
 split-index.c          |   8 ++--
 tree.c                 |   4 +-
 unpack-trees.c         |  27 ++++++++-----
 13 files changed, 166 insertions(+), 94 deletions(-)

diff --git a/apply.c b/apply.c
index 7e5792c996..123646e1aa 100644
--- a/apply.c
+++ b/apply.c
@@ -4090,12 +4090,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
+		ce = make_index_cache_entry(&result, patch->old_mode, oid.hash, name, 0, 0);
 		if (!ce)
-			return error(_("make_cache_entry failed for path '%s'"),
+			return error(_("make_index_cache_entry failed for path '%s'"),
 				     name);
 		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
-			free(ce);
+			discard_index_cache_entry(ce);
 			return error(_("could not add %s to temporary index"),
 				     name);
 		}
@@ -4263,12 +4263,11 @@ static int add_index_file(struct apply_state *state,
 	struct stat st;
 	struct cache_entry *ce;
 	int namelen = strlen(path);
-	unsigned ce_size = cache_entry_size(namelen);
 
 	if (!state->update_index)
 		return 0;
 
-	ce = xcalloc(1, ce_size);
+	ce = make_empty_index_cache_entry(&the_index, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(0);
@@ -4278,13 +4277,13 @@ static int add_index_file(struct apply_state *state,
 
 		if (!skip_prefix(buf, "Subproject commit ", &s) ||
 		    get_oid_hex(s, &ce->oid)) {
-			free(ce);
-		       return error(_("corrupt patch for submodule %s"), path);
+			discard_index_cache_entry(ce);
+			return error(_("corrupt patch for submodule %s"), path);
 		}
 	} else {
 		if (!state->cached) {
 			if (lstat(path, &st) < 0) {
-				free(ce);
+				discard_index_cache_entry(ce);
 				return error_errno(_("unable to stat newly "
 						     "created file '%s'"),
 						   path);
@@ -4292,13 +4291,13 @@ static int add_index_file(struct apply_state *state,
 			fill_stat_cache_info(ce, &st);
 		}
 		if (write_object_file(buf, size, blob_type, &ce->oid) < 0) {
-			free(ce);
+			discard_index_cache_entry(ce);
 			return error(_("unable to create backing store "
 				       "for newly created file %s"), path);
 		}
 	}
 	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-		free(ce);
+		discard_index_cache_entry(ce);
 		return error(_("unable to add cache entry for %s"), path);
 	}
 
@@ -4422,27 +4421,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
 				       struct patch *patch)
 {
 	int stage, namelen;
-	unsigned ce_size, mode;
+	unsigned mode;
 	struct cache_entry *ce;
 
 	if (!state->update_index)
 		return 0;
 	namelen = strlen(patch->new_name);
-	ce_size = cache_entry_size(namelen);
 	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
 
 	remove_file_from_cache(patch->new_name);
 	for (stage = 1; stage < 4; stage++) {
 		if (is_null_oid(&patch->threeway_stage[stage - 1]))
 			continue;
-		ce = xcalloc(1, ce_size);
+		ce = make_empty_index_cache_entry(&the_index, namelen);
 		memcpy(ce->name, patch->new_name, namelen);
 		ce->ce_mode = create_ce_mode(mode);
 		ce->ce_flags = create_ce_flags(stage);
 		ce->ce_namelen = namelen;
 		oidcpy(&ce->oid, &patch->threeway_stage[stage - 1]);
 		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-			free(ce);
+			discard_index_cache_entry(ce);
 			return error(_("unable to add cache entry for %s"),
 				     patch->new_name);
 		}
diff --git a/blame.c b/blame.c
index 78c9808bd1..8067e398a1 100644
--- a/blame.c
+++ b/blame.c
@@ -154,7 +154,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
 	time_t now;
-	int size, len;
+	int len;
 	struct cache_entry *ce;
 	unsigned mode;
 	struct strbuf msg = STRBUF_INIT;
@@ -252,8 +252,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 			/* Let's not bother reading from HEAD tree */
 			mode = S_IFREG | 0644;
 	}
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, &origin->blob_oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index b49b582071..a8af98e14c 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -77,7 +77,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_index_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -96,7 +96,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		if (ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			discard_index_cache_entry(ce);
 			return 0;
 		}
 	}
@@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_transient_cache_entry(mode, oid.hash, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	discard_transient_cache_entry(ce);
 	return status;
 }
 
diff --git a/builtin/difftool.c b/builtin/difftool.c
index aad0e073ee..8edcb1a8b6 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,10 +321,10 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ce = make_transient_cache_entry(mode, oid->hash, path, 0);
 	ret = checkout_entry(ce, state, NULL);
 
-	free(ce);
+	discard_transient_cache_entry(ce);
 	return ret;
 }
 
@@ -488,8 +488,8 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
-							 dst_path, 0, 0);
+					make_index_cache_entry(&wtindex, rmode, roid.hash,
+							       dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
 						ADD_CACHE_JUST_APPEND);
diff --git a/builtin/reset.c b/builtin/reset.c
index 7f1c3f02a3..1062dab73f 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,10 +134,10 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, one->oid.hash, one->path,
-				      0, 0);
+		ce = make_index_cache_entry(&the_index, one->mode, one->oid.hash, one->path,
+					    0, 0);
 		if (!ce)
-			die(_("make_cache_entry failed for path '%s'"),
+			die(_("make_index_cache_entry failed for path '%s'"),
 			    one->path);
 		if (is_missing) {
 			ce->ce_flags |= CE_INTENT_TO_ADD;
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 10d070a76f..2a7ab3cd7a 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -268,15 +268,14 @@ static int process_lstat_error(const char *path, int err)
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
-	int option, size;
+	int option;
 	struct cache_entry *ce;
 
 	/* Was the old index entry already up-to-date? */
 	if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
 		return 0;
 
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
@@ -285,13 +284,13 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 
 	if (index_path(&ce->oid, path, st,
 		       info_only ? 0 : HASH_WRITE_OBJECT)) {
-		free(ce);
+		discard_index_cache_entry(ce);
 		return -1;
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
 	if (add_cache_entry(ce, option)) {
-		free(ce);
+		discard_index_cache_entry(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
 	}
 	return 0;
@@ -403,15 +402,14 @@ static int process_path(const char *path)
 static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 			 const char *path, int stage)
 {
-	int size, len, option;
+	int len, option;
 	struct cache_entry *ce;
 
 	if (!verify_path(path))
 		return error("Invalid path '%s'", path);
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -589,7 +587,6 @@ static struct cache_entry *read_one_ent(const char *which,
 {
 	unsigned mode;
 	struct object_id oid;
-	int size;
 	struct cache_entry *ce;
 
 	if (get_tree_entry(ent, path, &oid, &mode)) {
@@ -602,8 +599,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, namelen);
 
 	oidcpy(&ce->oid, &oid);
 	memcpy(ce->name, path, namelen);
@@ -680,8 +676,8 @@ static int unresolve_one(const char *path)
 	error("%s: cannot add their version to the index.", path);
 	ret = -1;
  free_return:
-	free(ce_2);
-	free(ce_3);
+	discard_index_cache_entry(ce_2);
+	discard_index_cache_entry(ce_3);
 	return ret;
 }
 
@@ -748,7 +744,7 @@ static int do_reupdate(int ac, const char **av,
 					   ce->name, ce_namelen(ce), 0);
 		if (old && ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
-			free(old);
+			discard_index_cache_entry(old);
 			continue; /* unchanged */
 		}
 		/* Be careful.  The working tree may not have the
@@ -759,7 +755,7 @@ static int do_reupdate(int ac, const char **av,
 		path = xstrdup(ce->name);
 		update_one(path);
 		free(path);
-		free(old);
+		discard_index_cache_entry(old);
 		if (save_nr != active_nr)
 			goto redo;
 	}
diff --git a/cache.h b/cache.h
index 31f8f0420a..3760adbe25 100644
--- a/cache.h
+++ b/cache.h
@@ -339,6 +339,34 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 extern void free_name_hash(struct index_state *istate);
 
 
+/* Cache entry creation and freeing */
+
+/*
+ * Create cache_entry intended for use in the specified index. Caller
+ * is responsible for discarding the cache_entry with
+ * `discard_index_cache_entry`.
+ */
+extern struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
+extern struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t name_len);
+
+/*
+ * Create a cache_entry that is not intended to be added to an index.
+ * Caller is responsible for discarding the cache_entry
+ * with `discard_transient_cache_entry`.
+ */
+extern struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage);
+extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
+
+/*
+ * Discard cache entry allocated via `make_*_index_cache_entry`.
+ */
+void discard_index_cache_entry(struct cache_entry *ce);
+
+/*
+ * Discard cache entry allocated via `make_*_transient_cache_entry`.
+ */
+void discard_transient_cache_entry(struct cache_entry *ce);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
@@ -690,7 +718,6 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 693f60e0a3..be118c0c6d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -252,7 +252,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid->hash : null_sha1, path, stage, 0);
+	ce = make_index_cache_entry(&the_index, mode, oid ? oid->hash : null_sha1, path, stage, 0);
 	if (!ce)
 		return err(o, _("addinfo_cache failed for path '%s'"), path);
 
diff --git a/read-cache.c b/read-cache.c
index 2cb4f53b57..2a61cee130 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -61,7 +61,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 	replace_index_entry_in_base(istate, old, ce);
 	remove_name_hash(istate, old);
-	free(old);
+	discard_index_cache_entry(old);
 	ce->ce_flags &= ~CE_HASHED;
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +74,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new_entry = xmalloc(cache_entry_size(namelen));
+	new_entry = make_empty_index_cache_entry(istate, namelen);
 	copy_cache_entry(new_entry, old_entry);
 	new_entry->ce_flags &= ~CE_HASHED;
 	new_entry->ce_namelen = namelen;
@@ -623,7 +623,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new_entry = xcalloc(1, cache_entry_size(len));
+	new_entry = make_empty_index_cache_entry(istate, len);
 	memcpy(new_entry->name, alias->name, len);
 	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
@@ -640,7 +640,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-	int size, namelen, was_same;
+	int namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
@@ -662,8 +662,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_namelen = namelen;
 	if (!intent_only)
@@ -704,13 +703,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 				ce_mark_uptodate(alias);
 			alias->ce_flags |= CE_ADDED;
 
-			free(ce);
+			discard_index_cache_entry(ce);
 			return 0;
 		}
 	}
 	if (!intent_only) {
 		if (index_path(&ce->oid, path, st, newflags)) {
-			free(ce);
+			discard_index_cache_entry(ce);
 			return error("unable to index file %s", path);
 		}
 	} else
@@ -727,9 +726,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		    ce->ce_mode == alias->ce_mode);
 
 	if (pretend)
-		free(ce);
+		discard_index_cache_entry(ce);
 	else if (add_index_entry(istate, ce, add_option)) {
-		free(ce);
+		discard_index_cache_entry(ce);
 		return error("unable to add %s to index", path);
 	}
 	if (verbose && !was_same)
@@ -745,12 +744,22 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 	return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
-		const unsigned char *sha1, const char *path, int stage,
-		unsigned int refresh_options)
+struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_empty_transient_cache_entry(size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode,
+			    const unsigned char *sha1, const char *path,
+			    int stage, unsigned int refresh_options)
 {
-	int size, len;
 	struct cache_entry *ce, *ret;
+	int len;
 
 	if (!verify_path(path)) {
 		error("Invalid path '%s'", path);
@@ -758,8 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	}
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, len);
 
 	hashcpy(ce->oid.hash, sha1);
 	memcpy(ce->name, path, len);
@@ -769,10 +777,34 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 
 	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
-		free(ce);
+		discard_index_cache_entry(ce);
+
 	return ret;
 }
 
+struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1,
+			   const char *path, int stage)
+{
+	struct cache_entry *ce;
+	int len;
+
+	if (!verify_path(path)) {
+		error("Invalid path '%s'", path);
+		return NULL;
+	}
+
+	len = strlen(path);
+	ce = make_empty_transient_cache_entry(len);
+
+	hashcpy(ce->oid.hash, sha1);
+	memcpy(ce->name, path, len);
+	ce->ce_flags = create_ce_flags(stage);
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	return ce;
+}
+
 /*
  * Chmod an index entry with either +x or -x.
  *
@@ -1243,7 +1275,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
 	struct stat st;
 	struct cache_entry *updated;
-	int changed, size;
+	int changed;
 	int refresh = options & CE_MATCH_REFRESH;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
@@ -1323,8 +1355,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
-	size = ce_size(ce);
-	updated = xmalloc(size);
+	updated = make_empty_index_cache_entry(istate, ce_namelen(ce));
 	copy_cache_entry(updated, ce);
 	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
 	fill_stat_cache_info(updated, &st);
@@ -1610,12 +1641,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = xmalloc(cache_entry_size(len));
+	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1657,7 +1689,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *create_from_disk(struct index_state *istate,
+					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
 {
@@ -1688,13 +1721,13 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(ondisk, flags,
+		ce = cache_entry_from_ondisk(istate, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1826,7 +1859,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1932,7 +1965,7 @@ int discard_index(struct index_state *istate)
 		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
 		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
 			continue;
-		free(istate->cache[i]);
+		discard_index_cache_entry(istate->cache[i]);
 	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2622,14 +2655,13 @@ int read_index_unmerged(struct index_state *istate)
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i];
 		struct cache_entry *new_ce;
-		int size, len;
+		int len;
 
 		if (!ce_stage(ce))
 			continue;
 		unmerged = 1;
 		len = ce_namelen(ce);
-		size = cache_entry_size(len);
-		new_ce = xcalloc(1, size);
+		new_ce = make_empty_index_cache_entry(istate, len);
 		memcpy(new_ce->name, ce->name, len);
 		new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
 		new_ce->ce_namelen = len;
@@ -2738,3 +2770,16 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	dst->untracked = src->untracked;
 	src->untracked = NULL;
 }
+
+/*
+ * Free cache entry allocated for an index.
+ */
+void discard_index_cache_entry(struct cache_entry *ce)
+{
+	free(ce);
+}
+
+void discard_transient_cache_entry(struct cache_entry *ce)
+{
+	free(ce);
+}
diff --git a/resolve-undo.c b/resolve-undo.c
index aed95b4b35..96ef6307a6 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,8 +146,10 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], ru->oid[i].hash,
-				       name, i + 1, 0);
+		nce = make_index_cache_entry(istate,
+					     ru->mode[i],
+					     ru->oid[i].hash,
+					     name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
 		if (add_index_entry(istate, nce, ADD_CACHE_OK_TO_ADD)) {
diff --git a/split-index.c b/split-index.c
index 3eb8ff1b43..d3326d2645 100644
--- a/split-index.c
+++ b/split-index.c
@@ -123,7 +123,7 @@ static void replace_entry(size_t pos, void *data)
 	src->ce_flags |= CE_UPDATE_IN_BASE;
 	src->ce_namelen = dst->ce_namelen;
 	copy_cache_entry(dst, src);
-	free(src);
+	discard_index_cache_entry(src);
 	si->nr_replacements++;
 }
 
@@ -224,7 +224,7 @@ void prepare_to_write_split_index(struct index_state *istate)
 			base->ce_flags = base_flags;
 			if (ret)
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
-			free(base);
+			discard_index_cache_entry(base);
 			si->base->cache[ce->index - 1] = ce;
 		}
 		for (i = 0; i < si->base->cache_nr; i++) {
@@ -301,7 +301,7 @@ void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce
 	    ce == istate->split_index->base->cache[ce->index - 1])
 		ce->ce_flags |= CE_REMOVE;
 	else
-		free(ce);
+		discard_index_cache_entry(ce);
 }
 
 void replace_index_entry_in_base(struct index_state *istate,
@@ -314,7 +314,7 @@ void replace_index_entry_in_base(struct index_state *istate,
 	    old_entry->index <= istate->split_index->base->cache_nr) {
 		new_entry->index = old_entry->index;
 		if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
-			free(istate->split_index->base->cache[new_entry->index - 1]);
+			discard_index_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
 		istate->split_index->base->cache[new_entry->index - 1] = new_entry;
 	}
 }
diff --git a/tree.c b/tree.c
index 1c68ea586b..1ba39c9374 100644
--- a/tree.c
+++ b/tree.c
@@ -16,15 +16,13 @@ static int read_one_entry_opt(struct index_state *istate,
 			      unsigned mode, int stage, int opt)
 {
 	int len;
-	unsigned int size;
 	struct cache_entry *ce;
 
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 
 	len = strlen(pathname);
-	size = cache_entry_size(baselen + len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, baselen + len);
 
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(stage);
diff --git a/unpack-trees.c b/unpack-trees.c
index e73745051e..1ce6242f3e 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -192,10 +192,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce)
+static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
 {
 	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = xmalloc(size);
+	struct cache_entry *new_entry = make_empty_index_cache_entry(istate, ce_namelen(ce));
 
 	memcpy(new_entry, ce, size);
 	return new_entry;
@@ -205,7 +205,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce), set, clear);
+	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -786,10 +786,17 @@ static int ce_in_traverse_path(const struct cache_entry *ce,
 	return (info->pathlen < ce_namelen(ce));
 }
 
-static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
+static struct cache_entry *create_ce_entry(const struct traverse_info *info,
+	const struct name_entry *n,
+	int stage,
+	struct index_state *istate,
+	int is_transient)
 {
 	int len = traverse_path_len(info, n);
-	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
+	struct cache_entry *ce =
+		is_transient ?
+		make_empty_transient_cache_entry(len) :
+		make_empty_index_cache_entry(istate, len);
 
 	ce->ce_mode = create_ce_mode(n->mode);
 	ce->ce_flags = create_ce_flags(stage);
@@ -835,7 +842,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 			stage = 3;
 		else
 			stage = 2;
-		src[i + o->merge] = create_ce_entry(info, names + i, stage);
+		src[i + o->merge] = create_ce_entry(info, names + i, stage, &o->result, o->merge);
 	}
 
 	if (o->merge) {
@@ -844,7 +851,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		for (i = 0; i < n; i++) {
 			struct cache_entry *ce = src[i + o->merge];
 			if (ce != o->df_conflict_entry)
-				free(ce);
+				discard_transient_cache_entry(ce);
 		}
 		return rc;
 	}
@@ -1765,7 +1772,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce);
+	struct cache_entry *merge = dup_entry(ce, &o->result);
 
 	if (!old) {
 		/*
@@ -1785,7 +1792,7 @@ static int merged_entry(const struct cache_entry *ce,
 
 		if (verify_absent(merge,
 				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
-			free(merge);
+			discard_index_cache_entry(merge);
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
@@ -1811,7 +1818,7 @@ static int merged_entry(const struct cache_entry *ce,
 			update = 0;
 		} else {
 			if (verify_uptodate(old, o)) {
-				free(merge);
+				discard_index_cache_entry(merge);
 				return -1;
 			}
 			/* Migrate old flags over */
-- 
2.14.3

[PATCH v2 3/5] mem-pool: fill out functionality

[Jameson Miller]

Adds the following functionality to memory pools:

 - Lifecycle management functions (init, discard)

 - Test whether a memory location is part of the managed pool

 - Function to combine 2 pools

This also adds logic to track all memory allocations made by a memory
pool.

These functions will be used in a future commit in this commit series.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 mem-pool.h |  32 +++++++++++++++++
 2 files changed, 142 insertions(+), 4 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index 389d7af447..a495885c4b 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -5,6 +5,8 @@
 #include "cache.h"
 #include "mem-pool.h"
 
+#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
+
 static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
 {
 	struct mp_block *p;
@@ -19,6 +21,60 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 	return p;
 }
 
+static void *mem_pool_alloc_custom(struct mem_pool *mem_pool, size_t block_alloc)
+{
+	char *p;
+	ALLOC_GROW(mem_pool->custom, mem_pool->nr + 1, mem_pool->alloc);
+	ALLOC_GROW(mem_pool->custom_end, mem_pool->nr_end + 1, mem_pool->alloc_end);
+
+	p = xmalloc(block_alloc);
+	mem_pool->custom[mem_pool->nr++] = p;
+	mem_pool->custom_end[mem_pool->nr_end++] = p + block_alloc;
+
+	mem_pool->pool_alloc += block_alloc;
+
+	return mem_pool->custom[mem_pool->nr];
+}
+
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
+{
+	if (!(*mem_pool))
+	{
+		*mem_pool = xmalloc(sizeof(struct mem_pool));
+		(*mem_pool)->pool_alloc = 0;
+		(*mem_pool)->mp_block = NULL;
+		(*mem_pool)->block_alloc = BLOCK_GROWTH_SIZE;
+		(*mem_pool)->custom = NULL;
+		(*mem_pool)->nr = 0;
+		(*mem_pool)->alloc = 0;
+		(*mem_pool)->custom_end = NULL;
+		(*mem_pool)->nr_end = 0;
+		(*mem_pool)->alloc_end = 0;
+
+		if (initial_size > 0)
+			mem_pool_alloc_block(*mem_pool, initial_size);
+	}
+}
+
+void mem_pool_discard(struct mem_pool *mem_pool)
+{
+	int i;
+	struct mp_block *block, *block_to_free;
+	for (block = mem_pool->mp_block; block;)
+	{
+		block_to_free = block;
+		block = block->next_block;
+		free(block_to_free);
+	}
+
+	for (i = 0; i < mem_pool->nr; i++)
+		free(mem_pool->custom[i]);
+
+	free(mem_pool->custom);
+	free(mem_pool->custom_end);
+	free(mem_pool);
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p;
@@ -33,10 +89,8 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 			break;
 
 	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2)) {
-			mem_pool->pool_alloc += len;
-			return xmalloc(len);
-		}
+		if (len >= (mem_pool->block_alloc / 2))
+			return mem_pool_alloc_custom(mem_pool, len);
 
 		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
 	}
@@ -53,3 +107,55 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	memset(r, 0, len);
 	return r;
 }
+
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
+{
+	int i;
+	struct mp_block *p;
+
+	/* Check if memory is allocated in a block */
+	for (p = mem_pool->mp_block; p; p = p->next_block)
+		if ((mem >= ((void *)p->space)) &&
+		    (mem < ((void *)p->end)))
+			return 1;
+
+	/* Check if memory is allocated in custom block */
+	for (i = 0; i < mem_pool->nr; i++)
+		if ((mem >= mem_pool->custom[i]) &&
+		    (mem < mem_pool->custom_end[i]))
+			return 1;
+
+	return 0;
+}
+
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
+{
+	int i;
+	struct mp_block **tail = &dst->mp_block;
+
+	/* Find pointer of dst's last block (if any) */
+	while (*tail)
+		tail = &(*tail)->next_block;
+
+	/* Append the blocks from src to dst */
+	*tail = src->mp_block;
+
+	/* Combine custom allocations */
+	ALLOC_GROW(dst->custom, dst->nr + src->nr, dst->alloc);
+	ALLOC_GROW(dst->custom_end, dst->nr_end + src->nr_end, dst->alloc_end);
+
+	for (i = 0; i < src->nr; i++) {
+		dst->custom[dst->nr++] = src->custom[i];
+		dst->custom_end[dst->nr_end++] = src->custom_end[i];
+	}
+
+	dst->pool_alloc += src->pool_alloc;
+	src->pool_alloc = 0;
+	src->mp_block = NULL;
+	src->custom = NULL;
+	src->nr = 0;
+	src->alloc = 0;
+	src->custom_end = NULL;
+	src->nr_end = 0;
+	src->alloc_end = 0;
+}
diff --git a/mem-pool.h b/mem-pool.h
index 829ad58ecf..34df4fa709 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -19,8 +19,27 @@ struct mem_pool {
 
 	/* The total amount of memory allocated by the pool. */
 	size_t pool_alloc;
+
+	/*
+	 * Array of pointers to "custom size" memory allocations.
+	 * This is used for "large" memory allocations.
+	 * The *_end variables are used to track the range of memory
+	 * allocated.
+	 */
+	void **custom, **custom_end;
+	int nr, nr_end, alloc, alloc_end;
 };
 
+/*
+ * Initialize mem_pool specified initial.
+ */
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
+
+/*
+ * Discard a memory pool and free all the memory it is responsible for.
+ */
+void mem_pool_discard(struct mem_pool *mem_pool);
+
 /*
  * Alloc memory from the mem_pool.
  */
@@ -31,4 +50,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
+ * pool will be empty and not contain any memory. It still needs to be free'd
+ * with a call to `mem_pool_discard`.
+ */
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
+
+/*
+ * Check if a memory pointed at by 'mem' is part of the range of
+ * memory managed by the specified mem_pool.
+ */
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
+
 #endif
-- 
2.14.3

Re: [PATCH v2 3/5] mem-pool: fill out functionality

[Stefan Beller]

On Mon, Apr 30, 2018 at 8:31 AM, Jameson Miller <jamill@microsoft.com> wrote:
> Adds the following functionality to memory pools:
>
>  - Lifecycle management functions (init, discard)
>
>  - Test whether a memory location is part of the managed pool
>
>  - Function to combine 2 pools
>
> This also adds logic to track all memory allocations made by a memory
> pool.
>
> These functions will be used in a future commit in this commit series.
>
> Signed-off-by: Jameson Miller <jamill@microsoft.com>
> ---
>  mem-pool.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  mem-pool.h |  32 +++++++++++++++++

> diff --git a/mem-pool.h b/mem-pool.h
> index 829ad58ecf..34df4fa709 100644
> --- a/mem-pool.h
> +++ b/mem-pool.h
> @@ -19,8 +19,27 @@ struct mem_pool {
>
>         /* The total amount of memory allocated by the pool. */
>         size_t pool_alloc;
> +
> +       /*
> +        * Array of pointers to "custom size" memory allocations.
> +        * This is used for "large" memory allocations.
> +        * The *_end variables are used to track the range of memory
> +        * allocated.
> +        */
> +       void **custom, **custom_end;
> +       int nr, nr_end, alloc, alloc_end;
>  };

What is the design goal of this mem pool?
What is it really good at, which patterns of use should we avoid?

It looks like internally the mem-pool can either use mp_blocks
that are stored as a linked list, or it can have custom allocations
stored in an array.

Is the linked list or the custom part sorted by some key?
Does it need to be sorted?

I am currently looking at alloc.c, which is really good for
allocating memory for equally sized parts, i.e. it is very efficient
at providing memory for fixed sized structs. And on top of that
it is not tracking any memory as it relies on program termination
for cleanup.

This memory pool seems to be optimized for allocations of
varying sizes, some of them huge (to be stored in the custom
part) and most of them rather small as they go into the mp_blocks?

Thanks,
Stefan

RE: [PATCH v2 3/5] mem-pool: fill out functionality

[Jameson Miller]

Thank you for taking a look - I think these are good questions. Please let me know if you have further questions.

> -----Original Message-----
> From: Stefan Beller <sbeller@google.com>
> Sent: Monday, April 30, 2018 5:42 PM
> To: Jameson Miller <jamill@microsoft.com>
> Cc: git@vger.kernel.org; gitster@pobox.com; pclouds@gmail.com;
> jonathantanmy@google.com
> Subject: Re: [PATCH v2 3/5] mem-pool: fill out functionality
> 
> On Mon, Apr 30, 2018 at 8:31 AM, Jameson Miller <jamill@microsoft.com>
> wrote:
> > Adds the following functionality to memory pools:
> >
> >  - Lifecycle management functions (init, discard)
> >
> >  - Test whether a memory location is part of the managed pool
> >
> >  - Function to combine 2 pools
> >
> > This also adds logic to track all memory allocations made by a memory
> > pool.
> >
> > These functions will be used in a future commit in this commit series.
> >
> > Signed-off-by: Jameson Miller <jamill@microsoft.com>
> > ---
> >  mem-pool.c | 114
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
> >  mem-pool.h |  32 +++++++++++++++++
> 
> > diff --git a/mem-pool.h b/mem-pool.h
> > index 829ad58ecf..34df4fa709 100644
> > --- a/mem-pool.h
> > +++ b/mem-pool.h
> > @@ -19,8 +19,27 @@ struct mem_pool {
> >
> >         /* The total amount of memory allocated by the pool. */
> >         size_t pool_alloc;
> > +
> > +       /*
> > +        * Array of pointers to "custom size" memory allocations.
> > +        * This is used for "large" memory allocations.
> > +        * The *_end variables are used to track the range of memory
> > +        * allocated.
> > +        */
> > +       void **custom, **custom_end;
> > +       int nr, nr_end, alloc, alloc_end;
> >  };
> 
> What is the design goal of this mem pool?
> What is it really good at, which patterns of use should we avoid?
> 

This memory pool is designed to provide many small (small
compared to the memory pool block size) chunks of memory from a
larger block of allocated memory. This reduces the overhead of
performing many small memory allocations from the heap. In the
ideal case, we know the total amount of memory required, and the
pool can make a single allocation to satisfy that requirement,
and hand it out in chunks to consumers.

We should avoid making many large memory requests (large compared
to the memory pool block size), as these requests will be
fulfilled from individual memory allocations (i.e. the "custom"
allocations). While there is not a correctness issue here, it
will not perform as well when requests are fulfilled from the
internal memory blocks.

> It looks like internally the mem-pool can either use mp_blocks that are stored as
> a linked list, or it can have custom allocations stored in an array.
> 
> Is the linked list or the custom part sorted by some key?
> Does it need to be sorted?
> 
> I am currently looking at alloc.c, which is really good for allocating memory for
> equally sized parts, i.e. it is very efficient at providing memory for fixed sized
> structs. And on top of that it is not tracking any memory as it relies on program
> termination for cleanup.

The linked list is ordered in the order the blocks were allocated
in. The last allocated block will be the head of the linked
list. This means that most memory requests should be fulfilled by
the head block, reducing the need to iterate through the list to
find available memory.

The custom memory blocks are in their own list because they will
never contain any free memory. There is no need to include these
allocations in the list of blocks that could potentially have
free memory.

I expect this code would be efficient at allocating many equal
sized parts, as long as those parts are comparitively small
compared to the block size. In this case, you would never
allocate "custom" blocks, and the overwhelming majority of
allocations would come from the head block. If you know the total
amount of memory you will need, then you can size the memory pool
so all allocations come from the head block.

> 
> This memory pool seems to be optimized for allocations of varying sizes, some
> of them huge (to be stored in the custom
> part) and most of them rather small as they go into the mp_blocks?

I would say this memory pool is optimized for allocations of
varying sizes (although it should be pretty efficient when the
allocations are of the same size), but can handle the edge case
when there happens to be a need for a "huge allocation".
> 
> Thanks,
> Stefan

Re: [PATCH v2 3/5] mem-pool: fill out functionality

[Duy Nguyen]

Another I noticed in the jm/mem-pool series is this loop in mem_pool_alloc()

for (p = mem_pool->mp_block; p; p = p->next_block)
        if (p->end - p->next_free >= len)
                break;

You always go from the start (mp_block) but at some point those first
blocks are filled up and we don't really need to walk from the start
anymore. If we allow the mem-pool user to set a "minimum alloc" limit,
then we can determine if the remaining space in a block is not useful
for any future allocation, we can just skip it and start looking for
an available from a new pointer, avail_block or something.

I'm writing this with alloc.c in mind because we have a lot more
blocks to allocate there. Unlike read-cache, you can't really estimate
how many mp_blocks you're going to need. This linked list could become
long. And because alloc.c does fixed size allocation, we use up one
block after another and will never find free space in previous blocks.

On Mon, Apr 30, 2018 at 5:31 PM, Jameson Miller <jamill@microsoft.com> wrote:
> diff --git a/mem-pool.c b/mem-pool.c
> index 389d7af447..a495885c4b 100644
> --- a/mem-pool.c
> +++ b/mem-pool.c
> @@ -5,6 +5,8 @@
>  #include "cache.h"
>  #include "mem-pool.h"
>
> +#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);

#define BLOCK_GROWTH_SIZE (1024*1024 - sizeof(struct mp_block))

(wrapped in brackets and no trailing semicolon)

> +
>  static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
>  {
>         struct mp_block *p;
> @@ -19,6 +21,60 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
>         return p;
>  }
>
> +static void *mem_pool_alloc_custom(struct mem_pool *mem_pool, size_t block_alloc)
> +{
> +       char *p;

An empty line between variable declaration and function body would be nice.

> +       ALLOC_GROW(mem_pool->custom, mem_pool->nr + 1, mem_pool->alloc);
> +       ALLOC_GROW(mem_pool->custom_end, mem_pool->nr_end + 1, mem_pool->alloc_end);
> +

If you put both custom and custom_end in a struct, then you can grow
just one array (of the new struct) and have fewer support variables
like nr_end and alloc_end

The only downside that I can see is the potential padding between
struct increasing memory consumption here. but since you don't care
about reallocation cost (i.e. large memory allocations should be
rare), it probably  does not matter either.

But wait, can we just reuse struct mp_block for this? You allocate a
new mp_block (for just one allocation) as usual, then you can can
maintain a linked list of custom alloc in "struct mp_block
*mp_custom_block" or something. This way we can walk both bulk and
custom allocation the same way.

> +       p = xmalloc(block_alloc);
> +       mem_pool->custom[mem_pool->nr++] = p;
> +       mem_pool->custom_end[mem_pool->nr_end++] = p + block_alloc;
> +
> +       mem_pool->pool_alloc += block_alloc;
> +
> +       return mem_pool->custom[mem_pool->nr];
> +}
> +
> +void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
> +{
> +       if (!(*mem_pool))

I think (!*mem_pool) should be enough, although you could avoid the
operator precedence headache by doing

if (*mem_pool)
        return;

> +       {
> +               *mem_pool = xmalloc(sizeof(struct mem_pool));

I think we tend to do *mem_pool = xmalloc(sizeof(**mem_pool));

> +               (*mem_pool)->pool_alloc = 0;

Eghh.. perhaps just declare

struct mem_pool *pool;

then allocate a new memory to this, initialize everything and only do

*mem_pool = pool;

at the end? It's much less of this (*mem_pool)->

> +               (*mem_pool)->mp_block = NULL;

Just memset() it once (or use xcallo) and only initialize
non-zero/null fields afterwards.

> +               (*mem_pool)->block_alloc = BLOCK_GROWTH_SIZE;
> +               (*mem_pool)->custom = NULL;
> +               (*mem_pool)->nr = 0;
> +               (*mem_pool)->alloc = 0;
> +               (*mem_pool)->custom_end = NULL;
> +               (*mem_pool)->nr_end = 0;
> +               (*mem_pool)->alloc_end = 0;
> +
> +               if (initial_size > 0)
> +                       mem_pool_alloc_block(*mem_pool, initial_size);
> +       }
> +}
> +
> +void mem_pool_discard(struct mem_pool *mem_pool)
> +{
> +       int i;
> +       struct mp_block *block, *block_to_free;
> +       for (block = mem_pool->mp_block; block;)
> +       {
> +               block_to_free = block;
> +               block = block->next_block;
> +               free(block_to_free);
> +       }
> +
> +       for (i = 0; i < mem_pool->nr; i++)
> +               free(mem_pool->custom[i]);
> +
> +       free(mem_pool->custom);
> +       free(mem_pool->custom_end);
> +       free(mem_pool);
> +}
> +
>  void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
>  {
>         struct mp_block *p;
> @@ -33,10 +89,8 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
>                         break;
>
>         if (!p) {
> -               if (len >= (mem_pool->block_alloc / 2)) {
> -                       mem_pool->pool_alloc += len;
> -                       return xmalloc(len);
> -               }
> +               if (len >= (mem_pool->block_alloc / 2))
> +                       return mem_pool_alloc_custom(mem_pool, len);
>
>                 p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
>         }
> @@ -53,3 +107,55 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
>         memset(r, 0, len);
>         return r;
>  }
> +
> +int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
> +{
> +       int i;
> +       struct mp_block *p;
> +
> +       /* Check if memory is allocated in a block */
> +       for (p = mem_pool->mp_block; p; p = p->next_block)
> +               if ((mem >= ((void *)p->space)) &&
> +                   (mem < ((void *)p->end)))
> +                       return 1;
> +
> +       /* Check if memory is allocated in custom block */
> +       for (i = 0; i < mem_pool->nr; i++)
> +               if ((mem >= mem_pool->custom[i]) &&
> +                   (mem < mem_pool->custom_end[i]))
> +                       return 1;
> +
> +       return 0;
> +}
> +
> +void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
> +{
> +       int i;
> +       struct mp_block **tail = &dst->mp_block;
> +
> +       /* Find pointer of dst's last block (if any) */
> +       while (*tail)
> +               tail = &(*tail)->next_block;
> +
> +       /* Append the blocks from src to dst */
> +       *tail = src->mp_block;
> +
> +       /* Combine custom allocations */
> +       ALLOC_GROW(dst->custom, dst->nr + src->nr, dst->alloc);
> +       ALLOC_GROW(dst->custom_end, dst->nr_end + src->nr_end, dst->alloc_end);
> +
> +       for (i = 0; i < src->nr; i++) {
> +               dst->custom[dst->nr++] = src->custom[i];
> +               dst->custom_end[dst->nr_end++] = src->custom_end[i];
> +       }
> +
> +       dst->pool_alloc += src->pool_alloc;
> +       src->pool_alloc = 0;
> +       src->mp_block = NULL;
> +       src->custom = NULL;
> +       src->nr = 0;
> +       src->alloc = 0;
> +       src->custom_end = NULL;
> +       src->nr_end = 0;
> +       src->alloc_end = 0;
> +}
> diff --git a/mem-pool.h b/mem-pool.h
> index 829ad58ecf..34df4fa709 100644
> --- a/mem-pool.h
> +++ b/mem-pool.h
> @@ -19,8 +19,27 @@ struct mem_pool {
>
>         /* The total amount of memory allocated by the pool. */
>         size_t pool_alloc;
> +
> +       /*
> +        * Array of pointers to "custom size" memory allocations.
> +        * This is used for "large" memory allocations.
> +        * The *_end variables are used to track the range of memory
> +        * allocated.
> +        */
> +       void **custom, **custom_end;
> +       int nr, nr_end, alloc, alloc_end;
>  };
>
> +/*
> + * Initialize mem_pool specified initial.
> + */
> +void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
> +
> +/*
> + * Discard a memory pool and free all the memory it is responsible for.
> + */
> +void mem_pool_discard(struct mem_pool *mem_pool);
> +
>  /*
>   * Alloc memory from the mem_pool.
>   */
> @@ -31,4 +50,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
>   */
>  void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
>
> +/*
> + * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
> + * pool will be empty and not contain any memory. It still needs to be free'd
> + * with a call to `mem_pool_discard`.
> + */
> +void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
> +
> +/*
> + * Check if a memory pointed at by 'mem' is part of the range of
> + * memory managed by the specified mem_pool.
> + */
> +int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
> +
>  #endif
> --
> 2.14.3
>



-- 
Duy

[PATCH v2 4/5] block alloc: allocate cache entries from mem_pool

[Jameson Miller]

When reading large indexes from disk, a portion of the time is
dominated in malloc() calls. This can be mitigated by allocating a
large block of memory and manage it ourselves via memory pools.

This change moves the cache entry allocation to be on top of memory
pools.

Design:
The index_state struct will gain a notion of an associated memory_pool
from which cache_entries will be allocated from. When reading in the
index from disk, we have information on the number of entries and
their size, which can guide us in deciding how large our initial
memory allocation should be. When an index is discarded, the
associated memory_pool will be discarded as well - so the lifetime of
a cache_entry is tied to the lifetime of the index_state that it was
allocated for.

In the case of a Split Index, the following rules are followed. 1st,
some terminology is defined:

Terminology:
  - 'the_index': represents the logical view of the index

  - 'split_index': represents the "base" cache entries. Read from the
    split index file.

'the_index' can reference a single split_index, as well as
cache_entries from the split_index. `the_index` will be discarded
before the `split_index` is.  This means that when we are allocating
cache_entries in the presence of a split index, we need to allocate
the entries from the `split_index`'s memory pool.  This allows us to
follow the pattern that `the_index` can reference cache_entries from
the `split_index`, and that the cache_entries will not be freed while
they are still being referenced.

Alternatives:
The current design does not track whether a cache_entry is allocated
from a pool or not. Instead, it relies on the caller to know how the
cache_entry will be used and to handle its lifecyle appropriately,
including calling the correct free() method. Instead, we could include
a bit of information in the cache_entry (either a bit indicating
whether cache_entry was allocated from a pool or not, or possibly even
a pointer back to the allocating pool), which can then be used to make
informed decisions about these objects. The downside of this approach
is that the cache_entry type would need to grow to incorporate this
information.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h       |  2 ++
 read-cache.c  | 95 +++++++++++++++++++++++++++++++++++++++++++++--------------
 split-index.c | 23 +++++++++++++--
 3 files changed, 95 insertions(+), 25 deletions(-)

diff --git a/cache.h b/cache.h
index 3760adbe25..7ed68f28e0 100644
--- a/cache.h
+++ b/cache.h
@@ -15,6 +15,7 @@
 #include "path.h"
 #include "sha1-array.h"
 #include "repository.h"
+#include "mem-pool.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -328,6 +329,7 @@ struct index_state {
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
+	struct mem_pool *ce_mem_pool;
 };
 
 extern struct index_state the_index;
diff --git a/read-cache.c b/read-cache.c
index 2a61cee130..01cd7fea41 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -46,6 +46,42 @@
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
 		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
+
+/*
+ * This is a guess of an pathname in the index.  We use this for V4
+ * index files to guess the un-deltafied size of the index in memory
+ * because of pathname deltafication.  This is not required for V2/V3
+ * index formats because their pathnames are not compressed.  If the
+ * initial amount of memory set aside is not sufficient, the mem pool
+ * will allocate extra memory.
+ */
+#define CACHE_ENTRY_PATH_LENGTH 80
+
+static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	return mem_pool_alloc(mem_pool, cache_entry_size(len));
+}
+
+static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
+{
+	return mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
+}
+
+static struct mem_pool *find_mem_pool(struct index_state *istate)
+{
+	struct mem_pool **pool_ptr;
+
+	if (istate->split_index && istate->split_index->base)
+		pool_ptr = &istate->split_index->base->ce_mem_pool;
+	else
+		pool_ptr = &istate->ce_mem_pool;
+
+	if (!*pool_ptr)
+		mem_pool_init(pool_ptr, 0);
+
+	return *pool_ptr;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -746,7 +782,7 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 
 struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
 {
-	return xcalloc(1, cache_entry_size(len));
+	return mem_pool__ce_calloc(find_mem_pool(istate), len);
 }
 
 struct cache_entry *make_empty_transient_cache_entry(size_t len)
@@ -1641,13 +1677,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+static struct cache_entry *cache_entry_from_ondisk(struct mem_pool *mem_pool,
 						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
+	struct cache_entry *ce = mem_pool__ce_alloc(mem_pool, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1689,7 +1725,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct index_state *istate,
+static struct cache_entry *create_from_disk(struct mem_pool *mem_pool,
 					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
@@ -1721,13 +1757,13 @@ static struct cache_entry *create_from_disk(struct index_state *istate,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags,
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1801,6 +1837,22 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_fsmonitor(istate);
 }
 
+static size_t estimate_cache_size_from_compressed(unsigned int entries)
+{
+	return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_PATH_LENGTH);
+}
+
+static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
+{
+	long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
+
+	/*
+	 * Account for potential alignment differences.
+	 */
+	per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	return ondisk_size + entries * per_entry;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1847,10 +1899,15 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
 	istate->initialized = 1;
 
-	if (istate->version == 4)
+	if (istate->version == 4) {
 		previous_name = &previous_name_buf;
-	else
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size_from_compressed(istate->cache_nr));
+	} else {
 		previous_name = NULL;
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size(mmap_size, istate->cache_nr));
+	}
 
 	src_offset = sizeof(*hdr);
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -1859,7 +1916,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate->ce_mem_pool, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1956,17 +2013,6 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-	int i;
-
-	for (i = 0; i < istate->cache_nr; i++) {
-		if (istate->cache[i]->index &&
-		    istate->split_index &&
-		    istate->split_index->base &&
-		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-			continue;
-		discard_index_cache_entry(istate->cache[i]);
-	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -1980,6 +2026,12 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool);
+		istate->ce_mem_pool = NULL;
+	}
+
 	return 0;
 }
 
@@ -2772,11 +2824,10 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 }
 
 /*
- * Free cache entry allocated for an index.
+ * Indicate that a cache entry is no longer is use
  */
 void discard_index_cache_entry(struct cache_entry *ce)
 {
-	free(ce);
 }
 
 void discard_transient_cache_entry(struct cache_entry *ce)
diff --git a/split-index.c b/split-index.c
index d3326d2645..6d82c4e148 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,16 +73,31 @@ void move_cache_to_base_index(struct index_state *istate)
 	int i;
 
 	/*
-	 * do not delete old si->base, its index entries may be shared
-	 * with istate->cache[]. Accept a bit of leaking here because
-	 * this code is only used by short-lived update-index.
+	 * If there was a previous base index, then transfer ownership of allocated
+	 * entries to the parent index.
 	 */
+	if (si->base &&
+		si->base->ce_mem_pool) {
+
+		if (!istate->ce_mem_pool)
+			mem_pool_init(&istate->ce_mem_pool, 0);
+
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+	}
+
 	si->base = xcalloc(1, sizeof(*si->base));
 	si->base->version = istate->version;
 	/* zero timestamp disables racy test in ce_write_index() */
 	si->base->timestamp = istate->timestamp;
 	ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
 	si->base->cache_nr = istate->cache_nr;
+
+	/*
+	 * The mem_pool needs to move with the allocated entries.
+	 */
+	si->base->ce_mem_pool = istate->ce_mem_pool;
+	istate->ce_mem_pool = NULL;
+
 	COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
 	mark_base_index_entries(si->base);
 	for (i = 0; i < si->base->cache_nr; i++)
@@ -330,6 +345,8 @@ void add_split_index(struct index_state *istate)
 void remove_split_index(struct index_state *istate)
 {
 	if (istate->split_index) {
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+
 		/*
 		 * can't discard_split_index(&the_index); because that
 		 * will destroy split_index->base->cache[], which may
-- 
2.14.3

[PATCH v2 5/5] block alloc: add validations around cache_entry lifecyle

[Jameson Miller]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h      |  7 +++++++
 git.c        |  3 +++
 mem-pool.c   | 24 +++++++++++++++++++++++-
 mem-pool.h   |  2 ++
 read-cache.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/cache.h b/cache.h
index 7ed68f28e0..8f10f0649b 100644
--- a/cache.h
+++ b/cache.h
@@ -369,6 +369,13 @@ void discard_index_cache_entry(struct cache_entry *ce);
  */
 void discard_transient_cache_entry(struct cache_entry *ce);
 
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/git.c b/git.c
index f598fae7b7..28ec7a6c4f 100644
--- a/git.c
+++ b/git.c
@@ -347,7 +347,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index a495885c4b..77adb5d5b9 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -60,21 +60,43 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 {
 	int i;
 	struct mp_block *block, *block_to_free;
+	int invalidate_memory = should_validate_cache_entries();
+
 	for (block = mem_pool->mp_block; block;)
 	{
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
-	for (i = 0; i < mem_pool->nr; i++)
+	for (i = 0; i < mem_pool->nr; i++) {
+		memset(mem_pool->custom[i], 0xDD, ((char *)mem_pool->custom_end[i]) - ((char *)mem_pool->custom[i]));
 		free(mem_pool->custom[i]);
+	}
 
 	free(mem_pool->custom);
 	free(mem_pool->custom_end);
 	free(mem_pool);
 }
 
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p;
diff --git a/mem-pool.h b/mem-pool.h
index 34df4fa709..b1f9a920ba 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -63,4 +63,6 @@ void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
  */
 int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
 
+int should_validate_cache_entries(void);
+
 #endif
diff --git a/read-cache.c b/read-cache.c
index 01cd7fea41..e1dc9f7f33 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1270,6 +1270,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 {
 	int pos;
 
+	validate_cache_entries(istate);
+
 	if (option & ADD_CACHE_JUST_APPEND)
 		pos = istate->cache_nr;
 	else {
@@ -1290,6 +1292,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 			   istate->cache_nr - pos - 1);
 	set_index_entry(istate, pos, ce);
 	istate->cache_changed |= CE_ENTRY_ADDED;
+
+	validate_cache_entries(istate);
 	return 0;
 }
 
@@ -2013,6 +2017,8 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
+	validate_cache_entries(istate);
+
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -2035,6 +2041,43 @@ int discard_index(struct index_state *istate)
 	return 0;
 }
 
+
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+	int validate_index_cache_entries = should_validate_cache_entries();
+
+	if (!validate_index_cache_entries)
+		return;
+
+	if (!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2828,6 +2871,10 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
  */
 void discard_index_cache_entry(struct cache_entry *ce)
 {
+	int invalidate_cache_entry = should_validate_cache_entries();
+
+	if (ce && invalidate_cache_entry)
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
 }
 
 void discard_transient_cache_entry(struct cache_entry *ce)
-- 
2.14.3

Re: [PATCH v2 5/5] block alloc: add validations around cache_entry lifecyle

[Duy Nguyen]

On Mon, Apr 30, 2018 at 5:31 PM, Jameson Miller <jamill@microsoft.com> wrote:
> Add an option (controlled by an environment variable) perform extra
> validations on mem_pool allocated cache entries. When set:
>
>   1) Invalidate cache_entry memory when discarding cache_entry.
>
>   2) When discarding index_state struct, verify that all cache_entries
>      were allocated from expected mem_pool.
>
>   3) When discarding mem_pools, invalidate mem_pool memory.

On linux step 3 could be better achieved by allocating blocks with
mmap() and freeing them with munmap(). Access to already munmap()'d
blocks will result in segmentation fault regardless of values.  I
guess Windows also has something similar (I vaguely remember something
about "locking memory" and stuff, but my win32 knowledge is decade old
at this point)

(Actually with glibc on linux, i'm pretty sure mmap is already used
for large allocation so step 3 is achieved without doing anything; not
sure about other libc implementations)

> This should provide extra checks that mem_pools and their allocated
> cache_entries are being used as expected.
>
> Signed-off-by: Jameson Miller <jamill@microsoft.com>
> ---
>  cache.h      |  7 +++++++
>  git.c        |  3 +++
>  mem-pool.c   | 24 +++++++++++++++++++++++-
>  mem-pool.h   |  2 ++
>  read-cache.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 82 insertions(+), 1 deletion(-)
>
> diff --git a/cache.h b/cache.h
> index 7ed68f28e0..8f10f0649b 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -369,6 +369,13 @@ void discard_index_cache_entry(struct cache_entry *ce);
>   */
>  void discard_transient_cache_entry(struct cache_entry *ce);
>
> +/*
> + * Validate the cache entries in the index.  This is an internal
> + * consistency check that the cache_entry structs are allocated from
> + * the expected memory pool.
> + */
> +void validate_cache_entries(const struct index_state *istate);
> +
>  #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
>  #define active_cache (the_index.cache)
>  #define active_nr (the_index.cache_nr)
> diff --git a/git.c b/git.c
> index f598fae7b7..28ec7a6c4f 100644
> --- a/git.c
> +++ b/git.c
> @@ -347,7 +347,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
>
>         trace_argv_printf(argv, "trace: built-in: git");
>
> +       validate_cache_entries(&the_index);
>         status = p->fn(argc, argv, prefix);
> +       validate_cache_entries(&the_index);
> +
>         if (status)
>                 return status;
>
> diff --git a/mem-pool.c b/mem-pool.c
> index a495885c4b..77adb5d5b9 100644
> --- a/mem-pool.c
> +++ b/mem-pool.c
> @@ -60,21 +60,43 @@ void mem_pool_discard(struct mem_pool *mem_pool)
>  {
>         int i;
>         struct mp_block *block, *block_to_free;
> +       int invalidate_memory = should_validate_cache_entries();

Heh.. cache-entries logic should not enter mem-pool.c.

> +
>         for (block = mem_pool->mp_block; block;)
>         {
>                 block_to_free = block;
>                 block = block->next_block;
> +
> +               if (invalidate_memory)
> +                       memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
> +
>                 free(block_to_free);
>         }
>
> -       for (i = 0; i < mem_pool->nr; i++)
> +       for (i = 0; i < mem_pool->nr; i++) {
> +               memset(mem_pool->custom[i], 0xDD, ((char *)mem_pool->custom_end[i]) - ((char *)mem_pool->custom[i]));

"if (invalidate_memory)" missing

>                 free(mem_pool->custom[i]);
> +       }
>
>         free(mem_pool->custom);
>         free(mem_pool->custom_end);
>         free(mem_pool);
>  }
>
> +int should_validate_cache_entries(void)
> +{
> +       static int validate_index_cache_entries = -1;
> +
> +       if (validate_index_cache_entries < 0) {
> +               if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))

There's a safer version that you can use, get_env_bool()

> +                       validate_index_cache_entries = 1;
> +               else
> +                       validate_index_cache_entries = 0;
> +       }
> +
> +       return validate_index_cache_entries;
> +}
> +
>  void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
>  {
>         struct mp_block *p;
> diff --git a/mem-pool.h b/mem-pool.h
> index 34df4fa709..b1f9a920ba 100644
> --- a/mem-pool.h
> +++ b/mem-pool.h
> @@ -63,4 +63,6 @@ void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
>   */
>  int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
>
> +int should_validate_cache_entries(void);
> +
>  #endif
> diff --git a/read-cache.c b/read-cache.c
> index 01cd7fea41..e1dc9f7f33 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -1270,6 +1270,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
>  {
>         int pos;
>
> +       validate_cache_entries(istate);

Validating _all_ entries every time an entry is added sounds way too expensive.

> +
>         if (option & ADD_CACHE_JUST_APPEND)
>                 pos = istate->cache_nr;
>         else {
> @@ -1290,6 +1292,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
>                            istate->cache_nr - pos - 1);
>         set_index_entry(istate, pos, ce);
>         istate->cache_changed |= CE_ENTRY_ADDED;
> +
> +       validate_cache_entries(istate);
>         return 0;
>  }
>
> @@ -2013,6 +2017,8 @@ int is_index_unborn(struct index_state *istate)
>
>  int discard_index(struct index_state *istate)
>  {
> +       validate_cache_entries(istate);
> +
>         resolve_undo_clear_index(istate);
>         istate->cache_nr = 0;
>         istate->cache_changed = 0;
> @@ -2035,6 +2041,43 @@ int discard_index(struct index_state *istate)
>         return 0;
>  }
>
> +
> +/*
> + * Validate the cache entries of this index.
> + * All cache entries associated with this index
> + * should have been allocated by the memory pool
> + * associated with this index, or by a referenced
> + * split index.
> + */
> +void validate_cache_entries(const struct index_state *istate)
> +{
> +       int i;
> +       int validate_index_cache_entries = should_validate_cache_entries();
> +
> +       if (!validate_index_cache_entries)
> +               return;
> +
> +       if (!istate || !istate->initialized)
> +               return;
> +
> +       for (i = 0; i < istate->cache_nr; i++) {
> +               if (!istate) {
> +                       die("internal error: cache entry is not allocated from expected memory pool");
> +               } else if (!istate->ce_mem_pool ||
> +                       !mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
> +                       if (!istate->split_index ||
> +                               !istate->split_index->base ||
> +                               !istate->split_index->base->ce_mem_pool ||
> +                               !mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
> +                               die("internal error: cache entry is not allocated from expected memory pool");
> +                       }
> +               }
> +       }
> +
> +       if (istate->split_index)
> +               validate_cache_entries(istate->split_index->base);
> +}
> +
>  int unmerged_index(const struct index_state *istate)
>  {
>         int i;
> @@ -2828,6 +2871,10 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
>   */
>  void discard_index_cache_entry(struct cache_entry *ce)
>  {
> +       int invalidate_cache_entry = should_validate_cache_entries();
> +
> +       if (ce && invalidate_cache_entry)
> +               memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
>  }
>
>  void discard_transient_cache_entry(struct cache_entry *ce)
> --
> 2.14.3
>



-- 
Duy

Re: [PATCH v2 0/5] Allocate cache entries from memory pool

[Duy Nguyen]

On Mon, Apr 30, 2018 at 5:31 PM, Jameson Miller <jamill@microsoft.com> wrote:
> This patch series improves the performance of loading indexes by
> reducing the number of malloc() calls. Loading the index from disk is
> partly dominated by the time in malloc(), which is called for each
> index entry. This patch series reduces the number of times malloc() is
> called as part of loading the index, and instead allocates a block of
> memory upfront that is large enough to hold all of the cache entries,
> and chunks this memory itself. This change builds on [1].

I have only looked at the mem-pool related patches to see if
mem-pool.c is good enough to replace alloc.c. To me, it's a "yes"
after we optimize mem_pool_alloc() a bit (not that performance really
matters in alloc.c case, but that may be because it's already
blazingly fast that we never noticed about it).

I probably should look at read-cache.c changes too. Maybe later.
Although after the change to use xmalloc() per entry a few years(?)
ago, it should be straight forward to use a different memory
allocator.
-- 
Duy

Re: [PATCH v2 0/5] Allocate cache entries from memory pool

[Stefan Beller]

On Thu, May 3, 2018 at 9:35 AM, Duy Nguyen <pclouds@gmail.com> wrote:
> On Mon, Apr 30, 2018 at 5:31 PM, Jameson Miller <jamill@microsoft.com> wrote:
>> This patch series improves the performance of loading indexes by
>> reducing the number of malloc() calls. Loading the index from disk is
>> partly dominated by the time in malloc(), which is called for each
>> index entry. This patch series reduces the number of times malloc() is
>> called as part of loading the index, and instead allocates a block of
>> memory upfront that is large enough to hold all of the cache entries,
>> and chunks this memory itself. This change builds on [1].
>
> I have only looked at the mem-pool related patches to see if
> mem-pool.c is good enough to replace alloc.c. To me, it's a "yes"
> after we optimize mem_pool_alloc() a bit (not that performance really
> matters in alloc.c case, but that may be because it's already
> blazingly fast that we never noticed about it).

alloc.c was not just about speed, but mostly about dense packing?
855419f764a (Add specialized object allocator, 2006-06-19)

To me it is also a clear yes when it comes to combining these
two memory pools.

Re: [PATCH v2 0/5] Allocate cache entries from memory pool

[Duy Nguyen]

On Thu, May 3, 2018 at 7:21 PM, Stefan Beller <sbeller@google.com> wrote:
> On Thu, May 3, 2018 at 9:35 AM, Duy Nguyen <pclouds@gmail.com> wrote:
>> On Mon, Apr 30, 2018 at 5:31 PM, Jameson Miller <jamill@microsoft.com> wrote:
>>> This patch series improves the performance of loading indexes by
>>> reducing the number of malloc() calls. Loading the index from disk is
>>> partly dominated by the time in malloc(), which is called for each
>>> index entry. This patch series reduces the number of times malloc() is
>>> called as part of loading the index, and instead allocates a block of
>>> memory upfront that is large enough to hold all of the cache entries,
>>> and chunks this memory itself. This change builds on [1].
>>
>> I have only looked at the mem-pool related patches to see if
>> mem-pool.c is good enough to replace alloc.c. To me, it's a "yes"
>> after we optimize mem_pool_alloc() a bit (not that performance really
>> matters in alloc.c case, but that may be because it's already
>> blazingly fast that we never noticed about it).
>
> alloc.c was not just about speed, but mostly about dense packing?
> 855419f764a (Add specialized object allocator, 2006-06-19)

I know. I vaguely remembered Linus made that change but did not really
look it up :) That reference should be included when/if you switch
from alloc.c to mem-pool.c.

> To me it is also a clear yes when it comes to combining these
> two memory pools.

I also did not notice that jm/mem-pool already landed in master. Have
you tried measure (both memory usage and allocation speed) of it and
alloc.c? Just take some big repo as an example and do count-objects -v
to see how many blobs/trees/commits it has, then allocate the same
amount with both alloc.c and mem-pool.c and measure both speed/mem.
I'm pretty sure you're right that mem-pool.c is a clear yes. I was
just being more conservative because we do (slightly) change
allocator's behavior when we make the switch. But it's also very
likely that any performance difference will be insignificant.

I'm asking this because if mem-pool.c is a clear winner, you can start
to update you series to use it now and kill alloc.c in the process.

PS. Is Jeff back yet? I'm sure Junio is listening and all but I'm
afraid he's too busy being a maintainer so Jeff's opinion in this area
is really valuable. He has all the fun and weird use cases to play
with at github.
-- 
Duy

Re: [PATCH v2 0/5] Allocate cache entries from memory pool

[Stefan Beller]

On Thu, May 3, 2018 at 12:17 PM, Duy Nguyen <pclouds@gmail.com> wrote:
>
>> To me it is also a clear yes when it comes to combining these
>> two memory pools.
>
> I also did not notice that jm/mem-pool already landed in master.

Oh, thanks for telling! Now that I look at it, I am doubting it;

The reason for my doubt is the potential quadratic behavior for
new allocations, in mem_pool_alloc() we walk all mp_blocks to
see if we can fit the requested allocation in one of the later blocks.
So if we call mem_pool_alloc a million times, we get a O(n)
mp_blocks which we'd have to walk in each call.

However in alloc.c we do know that a slab is full as soon as we
look take the next slab. That is the beauty of knowing 'len' at
construction time of the allocator.

So I guess I'll just re-use the mp_block and introduce another
struct fixed_sized_mem_pool, which will not look into other mp_blocks
but the current.


> Have
> you tried measure (both memory usage and allocation speed) of it and
> alloc.c?

No, I was about to, but then started reading the code in an attempt to replace
alloc.c by a mempool and saw the quadratic behavior.

> Just take some big repo as an example and do count-objects -v
> to see how many blobs/trees/commits it has, then allocate the same
> amount with both alloc.c and mem-pool.c and measure both speed/mem.
> I'm pretty sure you're right that mem-pool.c is a clear yes. I was
> just being more conservative because we do (slightly) change
> allocator's behavior when we make the switch. But it's also very
> likely that any performance difference will be insignificant.
>
> I'm asking this because if mem-pool.c is a clear winner, you can start
> to update you series to use it now and kill alloc.c in the process.

I'll implement the fixed_sized_mem_pool and take some measurements.

>
> PS. Is Jeff back yet?

His last email on the public list is Apr 10th, stating that he'll be offline for
"a few weeks", in <20180406175349.GB32228@sigill.intra.peff.net> he
said the vacation part is 3 weeks. So I think he is done with vacation and
is just hiding to figure out a nice comeback. ;-)

> I'm sure Junio is listening and all but I'm
> afraid he's too busy being a maintainer so Jeff's opinion in this area
> is really valuable. He has all the fun and weird use cases to play
> with at github.

ok. I'll cc him for these patches.

Thanks,
Stefan

RE: [PATCH v2 0/5] Allocate cache entries from memory pool

[Jameson Miller]

> -----Original Message-----
> From: git-owner@vger.kernel.org <git-owner@vger.kernel.org> On Behalf Of
> Stefan Beller
> Sent: Thursday, May 3, 2018 4:59 PM
> To: Duy Nguyen <pclouds@gmail.com>
> Cc: Jameson Miller <jamill@microsoft.com>; git@vger.kernel.org;
> gitster@pobox.com; jonathantanmy@google.com
> Subject: Re: [PATCH v2 0/5] Allocate cache entries from memory pool
> 
> On Thu, May 3, 2018 at 12:17 PM, Duy Nguyen <pclouds@gmail.com> wrote:
> >
> >> To me it is also a clear yes when it comes to combining these two
> >> memory pools.
> >
> > I also did not notice that jm/mem-pool already landed in master.
> 
> Oh, thanks for telling! Now that I look at it, I am doubting it;
> 
> The reason for my doubt is the potential quadratic behavior for new allocations,
> in mem_pool_alloc() we walk all mp_blocks to see if we can fit the requested
> allocation in one of the later blocks.
> So if we call mem_pool_alloc a million times, we get a O(n) mp_blocks which
> we'd have to walk in each call.

With the current design, when a new mp_block is allocated, it is
placed at the head of the linked list. This means that the most
recently allocated mp_block is the 1st block that is
searched. The *vast* majority of allocations should be fulfilled
from this 1st block. It is only when the block is full that we
search other mp_blocks in the list. If this is a concern, I think
we have a couple low cost options to mitigate it (maybe a flag to
control whether we search past the 1st mp_block for space, or
logic to move blocks out of the search queue when they are
full or fall below a threshold for available space).

If this is of interest, I could contribute a patch to enable one
of these behaviors?

> 
> However in alloc.c we do know that a slab is full as soon as we look take the
> next slab. That is the beauty of knowing 'len' at construction time of the
> allocator.
> 
> So I guess I'll just re-use the mp_block and introduce another struct
> fixed_sized_mem_pool, which will not look into other mp_blocks but the
> current.
> 
> 
> > Have
> > you tried measure (both memory usage and allocation speed) of it and
> > alloc.c?
> 
> No, I was about to, but then started reading the code in an attempt to replace
> alloc.c by a mempool and saw the quadratic behavior.
> 
> > Just take some big repo as an example and do count-objects -v to see
> > how many blobs/trees/commits it has, then allocate the same amount
> > with both alloc.c and mem-pool.c and measure both speed/mem.
> > I'm pretty sure you're right that mem-pool.c is a clear yes. I was
> > just being more conservative because we do (slightly) change
> > allocator's behavior when we make the switch. But it's also very
> > likely that any performance difference will be insignificant.
> >
> > I'm asking this because if mem-pool.c is a clear winner, you can start
> > to update you series to use it now and kill alloc.c in the process.
> 
> I'll implement the fixed_sized_mem_pool and take some measurements.
> 
> >
> > PS. Is Jeff back yet?
> 
> His last email on the public list is Apr 10th, stating that he'll be offline for "a few
> weeks", in <20180406175349.GB32228@sigill.intra.peff.net> he said the
> vacation part is 3 weeks. So I think he is done with vacation and is just hiding to
> figure out a nice comeback. ;-)
> 
> > I'm sure Junio is listening and all but I'm afraid he's too busy being
> > a maintainer so Jeff's opinion in this area is really valuable. He has
> > all the fun and weird use cases to play with at github.
> 
> ok. I'll cc him for these patches.
> 
> Thanks,
> Stefan

[PATCH] alloc.c: replace alloc by mempool

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---

>> The reason for my doubt is the potential quadratic behavior for new allocations,
>> in mem_pool_alloc() we walk all mp_blocks to see if we can fit the requested
>> allocation in one of the later blocks.
>> So if we call mem_pool_alloc a million times, we get a O(n) mp_blocks which
>> we'd have to walk in each call.
>
> With the current design, when a new mp_block is allocated, it is
> placed at the head of the linked list. This means that the most
> recently allocated mp_block is the 1st block that is
> searched. The *vast* majority of allocations should be fulfilled
> from this 1st block. It is only when the block is full that we
> search other mp_blocks in the list.

I just measured on git.git and linux.git (both of which are not *huge* by
any standard, but should give a good indication. linux has  6M objects,
and when allocating 1024 at a time, we run into the new block allocation
~6000 times).

I could not measure any meaningful difference.

linux.git $ git count-objects -v
count: 0
size: 0
in-pack: 6036543
packs: 2
size-pack: 2492985
prune-packable: 0
garbage: 0
size-garbage: 0

(with this patch)
 Performance counter stats for '/u/git/git count-objects -v' (30 runs):

          2.123683      task-clock:u (msec)       #    0.831 CPUs utilized            ( +-  2.32% )
                 0      context-switches:u        #    0.000 K/sec                  
                 0      cpu-migrations:u          #    0.000 K/sec                  
               126      page-faults:u             #    0.059 M/sec                    ( +-  0.22% )
           895,900      cycles:u                  #    0.422 GHz                      ( +-  1.40% )
           976,596      instructions:u            #    1.09  insn per cycle           ( +-  0.01% )
           218,256      branches:u                #  102.772 M/sec                    ( +-  0.01% )
             8,331      branch-misses:u           #    3.82% of all branches          ( +-  0.61% )

       0.002556203 seconds time elapsed                                          ( +-  2.20% )

  Performance counter stats for 'git count-objects -v' (30 runs):

          2.410352      task-clock:u (msec)       #    0.801 CPUs utilized            ( +-  2.79% )
                 0      context-switches:u        #    0.000 K/sec                  
                 0      cpu-migrations:u          #    0.000 K/sec                  
               131      page-faults:u             #    0.054 M/sec                    ( +-  0.16% )
           993,301      cycles:u                  #    0.412 GHz                      ( +-  1.99% )
         1,087,428      instructions:u            #    1.09  insn per cycle           ( +-  0.02% )
           244,292      branches:u                #  101.351 M/sec                    ( +-  0.02% )
             9,264      branch-misses:u           #    3.79% of all branches          ( +-  0.57% )

       0.003010854 seconds time elapsed                                          ( +-  2.54% )

So I think we could just replace it for now and optimize again later, if it
turns out to be a problem. I think the easiest optimisation is to increase
the allocation size of having a lot more objects per mp_block.

> If this is a concern, I think
> we have a couple low cost options to mitigate it (maybe a flag to
> control whether we search past the 1st mp_block for space, or
> logic to move blocks out of the search queue when they are
> full or fall below a threshold for available space).

Instead of a flag I thought of its own struct with its own functions,
which would not just have a different searching behavior, but also
store the size in the struct such that you can just call
fixed_size_mem_pool_alloc(void) to get another pointer.
A flag might be more elegant.

>
> If this is of interest, I could contribute a patch to enable one
> of these behaviors?

I am tempted to just do away with alloc.c for now and use the mem-pool.

Thanks,
Stefan



 alloc.c | 60 +++++++++++----------------------------------------------
 1 file changed, 11 insertions(+), 49 deletions(-)

diff --git a/alloc.c b/alloc.c
index 12afadfacdd..bf003e161be 100644
--- a/alloc.c
+++ b/alloc.c
@@ -15,6 +15,7 @@
 #include "tree.h"
 #include "commit.h"
 #include "tag.h"
+#include "mem-pool.h"
 
 #define BLOCKING 1024
 
@@ -26,61 +27,39 @@ union any_object {
 	struct tag tag;
 };
 
-struct alloc_state {
-	int count; /* total number of nodes allocated */
-	int nr;    /* number of nodes left in current allocation */
-	void *p;   /* first free node in current allocation */
-};
-
-static inline void *alloc_node(struct alloc_state *s, size_t node_size)
-{
-	void *ret;
-
-	if (!s->nr) {
-		s->nr = BLOCKING;
-		s->p = xmalloc(BLOCKING * node_size);
-	}
-	s->nr--;
-	s->count++;
-	ret = s->p;
-	s->p = (char *)s->p + node_size;
-	memset(ret, 0, node_size);
-	return ret;
-}
-
-static struct alloc_state blob_state;
+static struct mem_pool blob_state = {NULL, sizeof(struct blob)*1024 - sizeof(struct mp_block), 0 };
 void *alloc_blob_node(void)
 {
-	struct blob *b = alloc_node(&blob_state, sizeof(struct blob));
+	struct blob *b = mem_pool_alloc(&blob_state, sizeof(struct blob));
 	b->object.type = OBJ_BLOB;
 	return b;
 }
 
-static struct alloc_state tree_state;
+static struct mem_pool tree_state = {NULL, sizeof(struct tree)*1024 - sizeof(struct mp_block), 0 };
 void *alloc_tree_node(void)
 {
-	struct tree *t = alloc_node(&tree_state, sizeof(struct tree));
+	struct tree *t = mem_pool_alloc(&tree_state, sizeof(struct tree));
 	t->object.type = OBJ_TREE;
 	return t;
 }
 
-static struct alloc_state tag_state;
+static struct mem_pool tag_state = {NULL, sizeof(struct tag)*1024 - sizeof(struct mp_block), 0 };
 void *alloc_tag_node(void)
 {
-	struct tag *t = alloc_node(&tag_state, sizeof(struct tag));
+	struct tag *t = mem_pool_alloc(&tag_state, sizeof(struct tag));
 	t->object.type = OBJ_TAG;
 	return t;
 }
 
-static struct alloc_state object_state;
+static struct mem_pool object_state = {NULL, sizeof(union any_object)*1024 - sizeof(struct mp_block), 0 };
 void *alloc_object_node(void)
 {
-	struct object *obj = alloc_node(&object_state, sizeof(union any_object));
+	struct object *obj = mem_pool_alloc(&object_state, sizeof(union any_object));
 	obj->type = OBJ_NONE;
 	return obj;
 }
 
-static struct alloc_state commit_state;
+static struct mem_pool commit_state = {NULL, sizeof(struct commit)*1024 - sizeof(struct mp_block), 0 };
 
 unsigned int alloc_commit_index(void)
 {
@@ -90,26 +69,9 @@ unsigned int alloc_commit_index(void)
 
 void *alloc_commit_node(void)
 {
-	struct commit *c = alloc_node(&commit_state, sizeof(struct commit));
+	struct commit *c = mem_pool_alloc(&commit_state, sizeof(struct commit));
 	c->object.type = OBJ_COMMIT;
 	c->index = alloc_commit_index();
 	return c;
 }
 
-static void report(const char *name, unsigned int count, size_t size)
-{
-	fprintf(stderr, "%10s: %8u (%"PRIuMAX" kB)\n",
-			name, count, (uintmax_t) size);
-}
-
-#define REPORT(name, type)	\
-    report(#name, name##_state.count, name##_state.count * sizeof(type) >> 10)
-
-void alloc_report(void)
-{
-	REPORT(blob, struct blob);
-	REPORT(tree, struct tree);
-	REPORT(commit, struct commit);
-	REPORT(tag, struct tag);
-	REPORT(object, union any_object);
-}
-- 
2.17.0.441.gb46fe60e1d-goog

Re: [PATCH] alloc.c: replace alloc by mempool

[Duy Nguyen]

On Fri, May 4, 2018 at 12:18 AM, Stefan Beller <sbeller@google.com> wrote:
> I just measured on git.git and linux.git (both of which are not *huge* by
> any standard, but should give a good indication. linux has  6M objects,
> and when allocating 1024 at a time, we run into the new block allocation
> ~6000 times).
>
> I could not measure any meaningful difference.
>
> linux.git $ git count-objects -v
> count: 0
> size: 0
> in-pack: 6036543
> packs: 2
> size-pack: 2492985
> prune-packable: 0
> garbage: 0
> size-garbage: 0
>
> (with this patch)
>  Performance counter stats for '/u/git/git count-objects -v' (30 runs):
>
>           2.123683      task-clock:u (msec)       #    0.831 CPUs utilized            ( +-  2.32% )
>                  0      context-switches:u        #    0.000 K/sec
>                  0      cpu-migrations:u          #    0.000 K/sec
>                126      page-faults:u             #    0.059 M/sec                    ( +-  0.22% )
>            895,900      cycles:u                  #    0.422 GHz                      ( +-  1.40% )
>            976,596      instructions:u            #    1.09  insn per cycle           ( +-  0.01% )
>            218,256      branches:u                #  102.772 M/sec                    ( +-  0.01% )
>              8,331      branch-misses:u           #    3.82% of all branches          ( +-  0.61% )
>
>        0.002556203 seconds time elapsed                                          ( +-  2.20% )
>
>   Performance counter stats for 'git count-objects -v' (30 runs):
>
>           2.410352      task-clock:u (msec)       #    0.801 CPUs utilized            ( +-  2.79% )
>                  0      context-switches:u        #    0.000 K/sec
>                  0      cpu-migrations:u          #    0.000 K/sec
>                131      page-faults:u             #    0.054 M/sec                    ( +-  0.16% )
>            993,301      cycles:u                  #    0.412 GHz                      ( +-  1.99% )
>          1,087,428      instructions:u            #    1.09  insn per cycle           ( +-  0.02% )
>            244,292      branches:u                #  101.351 M/sec                    ( +-  0.02% )
>              9,264      branch-misses:u           #    3.79% of all branches          ( +-  0.57% )
>
>        0.003010854 seconds time elapsed                                          ( +-  2.54% )
>
> So I think we could just replace it for now and optimize again later, if it
> turns out to be a problem. I think the easiest optimisation is to increase
> the allocation size of having a lot more objects per mp_block.

Yeah. I also tested this from a different angle: memory overhead. For
2M objects with one mp_block containing 1024 objects (same setting as
alloc.c), the overhead (not counting malloc() internal overhead) is
46KB and we don't have any extra overhead due to padding between
objects. This is true for all struct blob, commit, tree and tag. This
is really good. alloc.c has zero overhead when measured this way but
46KB is practically zero to me.
-- 
Duy

Re: [PATCH] alloc.c: replace alloc by mempool

[Junio C Hamano]

Duy Nguyen <pclouds@gmail.com> writes:

>> So I think we could just replace it for now and optimize again later, if it
>> turns out to be a problem. I think the easiest optimisation is to increase
>> the allocation size of having a lot more objects per mp_block.
>
> Yeah. I also tested this from a different angle: memory overhead. For
> 2M objects with one mp_block containing 1024 objects (same setting as
> alloc.c), the overhead (not counting malloc() internal overhead) is
> 46KB and we don't have any extra overhead due to padding between
> objects. This is true for all struct blob, commit, tree and tag. This
> is really good. alloc.c has zero overhead when measured this way but
> 46KB is practically zero to me.

Thanks.

The above in short sounds like arguing "replacing alloc.c internal
with mempool incurs negligible memory overhead and performance
degradation, but that can be optimized later".  It was unclear to me
why such a replacement needs to happen in the first place, though.
Without such a code churn, there won't be extra overhead or need to
fix it up later, no?

Re: [PATCH] alloc.c: replace alloc by mempool

[Stefan Beller]

On Mon, May 7, 2018 at 5:37 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Duy Nguyen <pclouds@gmail.com> writes:
>
>>> So I think we could just replace it for now and optimize again later, if it
>>> turns out to be a problem. I think the easiest optimisation is to increase
>>> the allocation size of having a lot more objects per mp_block.
>>
>> Yeah. I also tested this from a different angle: memory overhead. For
>> 2M objects with one mp_block containing 1024 objects (same setting as
>> alloc.c), the overhead (not counting malloc() internal overhead) is
>> 46KB and we don't have any extra overhead due to padding between
>> objects. This is true for all struct blob, commit, tree and tag. This
>> is really good. alloc.c has zero overhead when measured this way but
>> 46KB is practically zero to me.
>
> Thanks.
>
> The above in short sounds like arguing "replacing alloc.c internal
> with mempool incurs negligible memory overhead and performance
> degradation, but that can be optimized later".  It was unclear to me
> why such a replacement needs to happen in the first place, though.

The replacement with mem-pool might be easier than making sure
that alloc.c has no globals and handles allocations per repository
correctly. It would make the sb/object-store-alloc series shorter than
it currently is, and maybe easier to review the code.

However now that sb/object-store-alloc is rerolled with keeping
the logic of alloc.c and not replacing it with mem-pool, the only
reason would be ease of maintainability by less code
On the other hand we have different implementations of
lists, vectors and hashmaps, so having different memory
allocators doesn't hurt.

> Without such a code churn, there won't be extra overhead or need to
> fix it up later, no?

The original motivation is to get the object store on a per-repository
basis. It might be cheaper to use an existing 'objectified' code instead
of doing that again.

Re: [PATCH] alloc.c: replace alloc by mempool

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> The replacement with mem-pool might be easier than making sure
> that alloc.c has no globals and handles allocations per repository
> correctly. It would make the sb/object-store-alloc series shorter than
> it currently is, and maybe easier to review the code.
>
> However now that sb/object-store-alloc is rerolled with keeping
> the logic of alloc.c and not replacing it with mem-pool, the only
> reason would be ease of maintainability by less code

That is sensible considertation; the patch should be sold as such,
instead of with an empty log message as if the reasoning is obvious
to everybody without being told ;-)

[PATCH v3 0/7] allocate cache entries from memory pool

[Jameson Miller]

Changes from V2:

	- Tweak logic of finding available memory block for memory
          allocation
	
	  - Only search head block
	  
	- Tweaked handling of large memory allocations.
	
	  - Large blocks now tracked in same manner as "regular"
            blocks
	  
	  - Large blocks are placed at end of linked list of memory
            blocks

	- Cache_entry type gains notion of whether it was allocated
          from memory pool or not
	
	  - Collapsed cache_entry discard logic into single
            function. This should make code easier to maintain

	- Small tweaks based on V1 feedback

Base Ref: master
Web-Diff: git@github.com:jamill/git.git/commit/d608515f9e
Checkout: git fetch git@github.com:jamill/git.git users/jamill/block_allocation-v3 && git checkout d608515f9e


Jameson Miller (7):
  read-cache: teach refresh_cache_entry() to take istate
  block alloc: add lifecycle APIs for cache_entry structs
  mem-pool: only search head block for available space
  mem-pool: add lifecycle management functions
  mem-pool: fill out functionality
  block alloc: allocate cache entries from mem_pool
  block alloc: add validations around cache_entry lifecyle

 apply.c                |  26 +++--
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   8 +-
 builtin/reset.c        |   6 +-
 builtin/update-index.c |  26 +++--
 cache.h                |  53 +++++++++-
 fast-import.c          |   2 +-
 git.c                  |   3 +
 mem-pool.c             | 116 ++++++++++++++++++++--
 mem-pool.h             |  25 ++++-
 merge-recursive.c      |   4 +-
 read-cache.c           | 261 ++++++++++++++++++++++++++++++++++++++++---------
 resolve-undo.c         |   6 +-
 split-index.c          |  58 ++++++++---
 tree.c                 |   4 +-
 unpack-trees.c         |  38 +++----
 17 files changed, 514 insertions(+), 135 deletions(-)


base-commit: ccdcbd54c4475c2238b310f7113ab3075b5abc9c
-- 
2.14.3

[PATCH v3 1/7] read-cache: teach refresh_cache_entry() to take istate

[Jameson Miller]

Refactor refresh_cache_entry() to work on a specific index, instead of
implicitly using the_index. This is in preparation for making the
make_cache_entry function work on a specific index.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h           | 2 +-
 merge-recursive.c | 2 +-
 read-cache.c      | 7 ++++---
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/cache.h b/cache.h
index 0c1fb9fbcc..f0a407602c 100644
--- a/cache.h
+++ b/cache.h
@@ -744,7 +744,7 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 #define REFRESH_IGNORE_SUBMODULES	0x0010	/* ignore submodules */
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
-extern struct cache_entry *refresh_cache_entry(struct cache_entry *, unsigned int);
+extern struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 /*
  * Opportunistically update the index but do not complain if we can't.
diff --git a/merge-recursive.c b/merge-recursive.c
index 0c0d48624d..693f60e0a3 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -260,7 +260,7 @@ static int add_cacheinfo(struct merge_options *o,
 	if (refresh) {
 		struct cache_entry *nce;
 
-		nce = refresh_cache_entry(ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		nce = refresh_cache_entry(&the_index, ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
 		if (!nce)
 			return err(o, _("addinfo_cache failed for path '%s'"), path);
 		if (nce != ce)
diff --git a/read-cache.c b/read-cache.c
index 10f1c6bb8a..2cb4f53b57 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -767,7 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	ce->ce_namelen = len;
 	ce->ce_mode = create_ce_mode(mode);
 
-	ret = refresh_cache_entry(ce, refresh_options);
+	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
 		free(ce);
 	return ret;
@@ -1448,10 +1448,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	return has_errors;
 }
 
-struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+					       struct cache_entry *ce,
 					       unsigned int options)
 {
-	return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
-- 
2.14.3

Re: [PATCH v3 1/7] read-cache: teach refresh_cache_entry() to take istate

[Stefan Beller]

On Wed, May 23, 2018 at 7:47 AM, Jameson Miller <jamill@microsoft.com> wrote:
> Refactor refresh_cache_entry() to work on a specific index, instead of
> implicitly using the_index. This is in preparation for making the
> make_cache_entry function work on a specific index.
>
> Signed-off-by: Jameson Miller <jamill@microsoft.com>

Reviewed-by: Stefan Beller <sbeller@google.com>

[PATCH v3 2/7] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

Add an API around managing the lifetime of cache_entry
structs. Abstracting memory management details behind an API will
allow for alternative memory management strategies without affecting
all the call sites.  This commit does not change how memory is
allocated / freed. A later commit in this series will allocate cache
entries from memory pools as appropriate.

Motivation:
It has been observed that the time spent loading an index with a large
number of entries is partly dominated by malloc() calls. This change
is in preparation for using memory pools to reduce the number of
malloc() calls made when loading an index.

This API makes a distinction between cache entries that are intended
for use with a particular index and cache entries that are not. This
enables us to use the knowledge about how a cache entry will be used
to make informed decisions about how to handle the corresponding
memory.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 apply.c                |  26 ++++++-------
 blame.c                |   5 +--
 builtin/checkout.c     |   8 ++--
 builtin/difftool.c     |   8 ++--
 builtin/reset.c        |   6 +--
 builtin/update-index.c |  26 ++++++-------
 cache.h                |  24 +++++++++++-
 merge-recursive.c      |   2 +-
 read-cache.c           | 100 ++++++++++++++++++++++++++++++++++---------------
 resolve-undo.c         |   6 ++-
 split-index.c          |   8 ++--
 tree.c                 |   4 +-
 unpack-trees.c         |  33 +++++++++++-----
 13 files changed, 162 insertions(+), 94 deletions(-)

diff --git a/apply.c b/apply.c
index 7e5792c996..b769fe0d15 100644
--- a/apply.c
+++ b/apply.c
@@ -4090,12 +4090,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
+		ce = make_index_cache_entry(&result, patch->old_mode, oid.hash, name, 0, 0);
 		if (!ce)
-			return error(_("make_cache_entry failed for path '%s'"),
+			return error(_("make_index_cache_entry failed for path '%s'"),
 				     name);
 		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("could not add %s to temporary index"),
 				     name);
 		}
@@ -4263,12 +4263,11 @@ static int add_index_file(struct apply_state *state,
 	struct stat st;
 	struct cache_entry *ce;
 	int namelen = strlen(path);
-	unsigned ce_size = cache_entry_size(namelen);
 
 	if (!state->update_index)
 		return 0;
 
-	ce = xcalloc(1, ce_size);
+	ce = make_empty_index_cache_entry(&the_index, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(0);
@@ -4278,13 +4277,13 @@ static int add_index_file(struct apply_state *state,
 
 		if (!skip_prefix(buf, "Subproject commit ", &s) ||
 		    get_oid_hex(s, &ce->oid)) {
-			free(ce);
-		       return error(_("corrupt patch for submodule %s"), path);
+			discard_cache_entry(ce);
+			return error(_("corrupt patch for submodule %s"), path);
 		}
 	} else {
 		if (!state->cached) {
 			if (lstat(path, &st) < 0) {
-				free(ce);
+				discard_cache_entry(ce);
 				return error_errno(_("unable to stat newly "
 						     "created file '%s'"),
 						   path);
@@ -4292,13 +4291,13 @@ static int add_index_file(struct apply_state *state,
 			fill_stat_cache_info(ce, &st);
 		}
 		if (write_object_file(buf, size, blob_type, &ce->oid) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to create backing store "
 				       "for newly created file %s"), path);
 		}
 	}
 	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error(_("unable to add cache entry for %s"), path);
 	}
 
@@ -4422,27 +4421,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
 				       struct patch *patch)
 {
 	int stage, namelen;
-	unsigned ce_size, mode;
+	unsigned mode;
 	struct cache_entry *ce;
 
 	if (!state->update_index)
 		return 0;
 	namelen = strlen(patch->new_name);
-	ce_size = cache_entry_size(namelen);
 	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
 
 	remove_file_from_cache(patch->new_name);
 	for (stage = 1; stage < 4; stage++) {
 		if (is_null_oid(&patch->threeway_stage[stage - 1]))
 			continue;
-		ce = xcalloc(1, ce_size);
+		ce = make_empty_index_cache_entry(&the_index, namelen);
 		memcpy(ce->name, patch->new_name, namelen);
 		ce->ce_mode = create_ce_mode(mode);
 		ce->ce_flags = create_ce_flags(stage);
 		ce->ce_namelen = namelen;
 		oidcpy(&ce->oid, &patch->threeway_stage[stage - 1]);
 		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to add cache entry for %s"),
 				     patch->new_name);
 		}
diff --git a/blame.c b/blame.c
index 78c9808bd1..8067e398a1 100644
--- a/blame.c
+++ b/blame.c
@@ -154,7 +154,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
 	time_t now;
-	int size, len;
+	int len;
 	struct cache_entry *ce;
 	unsigned mode;
 	struct strbuf msg = STRBUF_INIT;
@@ -252,8 +252,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 			/* Let's not bother reading from HEAD tree */
 			mode = S_IFREG | 0644;
 	}
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, &origin->blob_oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index b49b582071..1b7c90b418 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -77,7 +77,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_index_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -96,7 +96,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		if (ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
@@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_transient_cache_entry(mode, oid.hash, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	discard_cache_entry(ce);
 	return status;
 }
 
diff --git a/builtin/difftool.c b/builtin/difftool.c
index aad0e073ee..0289b9c62b 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,10 +321,10 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ce = make_transient_cache_entry(mode, oid->hash, path, 0);
 	ret = checkout_entry(ce, state, NULL);
 
-	free(ce);
+	discard_cache_entry(ce);
 	return ret;
 }
 
@@ -488,8 +488,8 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
-							 dst_path, 0, 0);
+					make_index_cache_entry(&wtindex, rmode, roid.hash,
+							       dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
 						ADD_CACHE_JUST_APPEND);
diff --git a/builtin/reset.c b/builtin/reset.c
index 7f1c3f02a3..1062dab73f 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,10 +134,10 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, one->oid.hash, one->path,
-				      0, 0);
+		ce = make_index_cache_entry(&the_index, one->mode, one->oid.hash, one->path,
+					    0, 0);
 		if (!ce)
-			die(_("make_cache_entry failed for path '%s'"),
+			die(_("make_index_cache_entry failed for path '%s'"),
 			    one->path);
 		if (is_missing) {
 			ce->ce_flags |= CE_INTENT_TO_ADD;
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 10d070a76f..7ea8aeecc4 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -268,15 +268,14 @@ static int process_lstat_error(const char *path, int err)
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
-	int option, size;
+	int option;
 	struct cache_entry *ce;
 
 	/* Was the old index entry already up-to-date? */
 	if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
 		return 0;
 
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
@@ -285,13 +284,13 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 
 	if (index_path(&ce->oid, path, st,
 		       info_only ? 0 : HASH_WRITE_OBJECT)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return -1;
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
 	if (add_cache_entry(ce, option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
 	}
 	return 0;
@@ -403,15 +402,14 @@ static int process_path(const char *path)
 static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 			 const char *path, int stage)
 {
-	int size, len, option;
+	int len, option;
 	struct cache_entry *ce;
 
 	if (!verify_path(path))
 		return error("Invalid path '%s'", path);
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -589,7 +587,6 @@ static struct cache_entry *read_one_ent(const char *which,
 {
 	unsigned mode;
 	struct object_id oid;
-	int size;
 	struct cache_entry *ce;
 
 	if (get_tree_entry(ent, path, &oid, &mode)) {
@@ -602,8 +599,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(&the_index, namelen);
 
 	oidcpy(&ce->oid, &oid);
 	memcpy(ce->name, path, namelen);
@@ -680,8 +676,8 @@ static int unresolve_one(const char *path)
 	error("%s: cannot add their version to the index.", path);
 	ret = -1;
  free_return:
-	free(ce_2);
-	free(ce_3);
+	discard_cache_entry(ce_2);
+	discard_cache_entry(ce_3);
 	return ret;
 }
 
@@ -748,7 +744,7 @@ static int do_reupdate(int ac, const char **av,
 					   ce->name, ce_namelen(ce), 0);
 		if (old && ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
-			free(old);
+			discard_cache_entry(old);
 			continue; /* unchanged */
 		}
 		/* Be careful.  The working tree may not have the
@@ -759,7 +755,7 @@ static int do_reupdate(int ac, const char **av,
 		path = xstrdup(ce->name);
 		update_one(path);
 		free(path);
-		free(old);
+		discard_cache_entry(old);
 		if (save_nr != active_nr)
 			goto redo;
 	}
diff --git a/cache.h b/cache.h
index f0a407602c..204f788438 100644
--- a/cache.h
+++ b/cache.h
@@ -339,6 +339,29 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 extern void free_name_hash(struct index_state *istate);
 
 
+/* Cache entry creation and freeing */
+
+/*
+ * Create cache_entry intended for use in the specified index. Caller
+ * is responsible for discarding the cache_entry with
+ * `discard_cache_entry`.
+ */
+extern struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
+extern struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t name_len);
+
+/*
+ * Create a cache_entry that is not intended to be added to an index.
+ * Caller is responsible for discarding the cache_entry
+ * with `discard_cache_entry`.
+ */
+extern struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage);
+extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
+
+/*
+ * Discard cache entry.
+ */
+void discard_cache_entry(struct cache_entry *ce);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
@@ -691,7 +714,6 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 693f60e0a3..be118c0c6d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -252,7 +252,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid->hash : null_sha1, path, stage, 0);
+	ce = make_index_cache_entry(&the_index, mode, oid ? oid->hash : null_sha1, path, stage, 0);
 	if (!ce)
 		return err(o, _("addinfo_cache failed for path '%s'"), path);
 
diff --git a/read-cache.c b/read-cache.c
index 2cb4f53b57..d51cc83312 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -61,7 +61,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 	replace_index_entry_in_base(istate, old, ce);
 	remove_name_hash(istate, old);
-	free(old);
+	discard_cache_entry(old);
 	ce->ce_flags &= ~CE_HASHED;
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +74,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new_entry = xmalloc(cache_entry_size(namelen));
+	new_entry = make_empty_index_cache_entry(istate, namelen);
 	copy_cache_entry(new_entry, old_entry);
 	new_entry->ce_flags &= ~CE_HASHED;
 	new_entry->ce_namelen = namelen;
@@ -623,7 +623,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new_entry = xcalloc(1, cache_entry_size(len));
+	new_entry = make_empty_index_cache_entry(istate, len);
 	memcpy(new_entry->name, alias->name, len);
 	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
@@ -640,7 +640,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-	int size, namelen, was_same;
+	int namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
@@ -662,8 +662,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_namelen = namelen;
 	if (!intent_only)
@@ -704,13 +703,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 				ce_mark_uptodate(alias);
 			alias->ce_flags |= CE_ADDED;
 
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
 	if (!intent_only) {
 		if (index_path(&ce->oid, path, st, newflags)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error("unable to index file %s", path);
 		}
 	} else
@@ -727,9 +726,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		    ce->ce_mode == alias->ce_mode);
 
 	if (pretend)
-		free(ce);
+		discard_cache_entry(ce);
 	else if (add_index_entry(istate, ce, add_option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("unable to add %s to index", path);
 	}
 	if (verbose && !was_same)
@@ -745,12 +744,22 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 	return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
-		const unsigned char *sha1, const char *path, int stage,
-		unsigned int refresh_options)
+struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_empty_transient_cache_entry(size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode,
+			    const unsigned char *sha1, const char *path,
+			    int stage, unsigned int refresh_options)
 {
-	int size, len;
 	struct cache_entry *ce, *ret;
+	int len;
 
 	if (!verify_path(path)) {
 		error("Invalid path '%s'", path);
@@ -758,8 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	}
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, len);
 
 	hashcpy(ce->oid.hash, sha1);
 	memcpy(ce->name, path, len);
@@ -769,10 +777,34 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 
 	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
-		free(ce);
+		discard_cache_entry(ce);
+
 	return ret;
 }
 
+struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1,
+			   const char *path, int stage)
+{
+	struct cache_entry *ce;
+	int len;
+
+	if (!verify_path(path)) {
+		error("Invalid path '%s'", path);
+		return NULL;
+	}
+
+	len = strlen(path);
+	ce = make_empty_transient_cache_entry(len);
+
+	hashcpy(ce->oid.hash, sha1);
+	memcpy(ce->name, path, len);
+	ce->ce_flags = create_ce_flags(stage);
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	return ce;
+}
+
 /*
  * Chmod an index entry with either +x or -x.
  *
@@ -1243,7 +1275,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
 	struct stat st;
 	struct cache_entry *updated;
-	int changed, size;
+	int changed;
 	int refresh = options & CE_MATCH_REFRESH;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
@@ -1323,8 +1355,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
-	size = ce_size(ce);
-	updated = xmalloc(size);
+	updated = make_empty_index_cache_entry(istate, ce_namelen(ce));
 	copy_cache_entry(updated, ce);
 	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
 	fill_stat_cache_info(updated, &st);
@@ -1610,12 +1641,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = xmalloc(cache_entry_size(len));
+	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1657,7 +1689,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *create_from_disk(struct index_state *istate,
+					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
 {
@@ -1688,13 +1721,13 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(ondisk, flags,
+		ce = cache_entry_from_ondisk(istate, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1826,7 +1859,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1932,7 +1965,7 @@ int discard_index(struct index_state *istate)
 		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
 		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
 			continue;
-		free(istate->cache[i]);
+		discard_cache_entry(istate->cache[i]);
 	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2622,14 +2655,13 @@ int read_index_unmerged(struct index_state *istate)
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i];
 		struct cache_entry *new_ce;
-		int size, len;
+		int len;
 
 		if (!ce_stage(ce))
 			continue;
 		unmerged = 1;
 		len = ce_namelen(ce);
-		size = cache_entry_size(len);
-		new_ce = xcalloc(1, size);
+		new_ce = make_empty_index_cache_entry(istate, len);
 		memcpy(new_ce->name, ce->name, len);
 		new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
 		new_ce->ce_namelen = len;
@@ -2738,3 +2770,11 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	dst->untracked = src->untracked;
 	src->untracked = NULL;
 }
+
+/*
+ * Free cache entry.
+ */
+void discard_cache_entry(struct cache_entry *ce)
+{
+	free(ce);
+}
diff --git a/resolve-undo.c b/resolve-undo.c
index aed95b4b35..96ef6307a6 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,8 +146,10 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], ru->oid[i].hash,
-				       name, i + 1, 0);
+		nce = make_index_cache_entry(istate,
+					     ru->mode[i],
+					     ru->oid[i].hash,
+					     name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
 		if (add_index_entry(istate, nce, ADD_CACHE_OK_TO_ADD)) {
diff --git a/split-index.c b/split-index.c
index 3eb8ff1b43..ab638b844d 100644
--- a/split-index.c
+++ b/split-index.c
@@ -123,7 +123,7 @@ static void replace_entry(size_t pos, void *data)
 	src->ce_flags |= CE_UPDATE_IN_BASE;
 	src->ce_namelen = dst->ce_namelen;
 	copy_cache_entry(dst, src);
-	free(src);
+	discard_cache_entry(src);
 	si->nr_replacements++;
 }
 
@@ -224,7 +224,7 @@ void prepare_to_write_split_index(struct index_state *istate)
 			base->ce_flags = base_flags;
 			if (ret)
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
-			free(base);
+			discard_cache_entry(base);
 			si->base->cache[ce->index - 1] = ce;
 		}
 		for (i = 0; i < si->base->cache_nr; i++) {
@@ -301,7 +301,7 @@ void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce
 	    ce == istate->split_index->base->cache[ce->index - 1])
 		ce->ce_flags |= CE_REMOVE;
 	else
-		free(ce);
+		discard_cache_entry(ce);
 }
 
 void replace_index_entry_in_base(struct index_state *istate,
@@ -314,7 +314,7 @@ void replace_index_entry_in_base(struct index_state *istate,
 	    old_entry->index <= istate->split_index->base->cache_nr) {
 		new_entry->index = old_entry->index;
 		if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
-			free(istate->split_index->base->cache[new_entry->index - 1]);
+			discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
 		istate->split_index->base->cache[new_entry->index - 1] = new_entry;
 	}
 }
diff --git a/tree.c b/tree.c
index 1c68ea586b..1ba39c9374 100644
--- a/tree.c
+++ b/tree.c
@@ -16,15 +16,13 @@ static int read_one_entry_opt(struct index_state *istate,
 			      unsigned mode, int stage, int opt)
 {
 	int len;
-	unsigned int size;
 	struct cache_entry *ce;
 
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 
 	len = strlen(pathname);
-	size = cache_entry_size(baselen + len);
-	ce = xcalloc(1, size);
+	ce = make_empty_index_cache_entry(istate, baselen + len);
 
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(stage);
diff --git a/unpack-trees.c b/unpack-trees.c
index dec37ad1e7..dd4d12ba45 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -192,10 +192,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce)
+static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
 {
 	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = xmalloc(size);
+	struct cache_entry *new_entry = make_empty_index_cache_entry(istate, ce_namelen(ce));
 
 	memcpy(new_entry, ce, size);
 	return new_entry;
@@ -205,7 +205,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce), set, clear);
+	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -786,10 +786,17 @@ static int ce_in_traverse_path(const struct cache_entry *ce,
 	return (info->pathlen < ce_namelen(ce));
 }
 
-static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
+static struct cache_entry *create_ce_entry(const struct traverse_info *info,
+	const struct name_entry *n,
+	int stage,
+	struct index_state *istate,
+	int is_transient)
 {
 	int len = traverse_path_len(info, n);
-	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
+	struct cache_entry *ce =
+		is_transient ?
+		make_empty_transient_cache_entry(len) :
+		make_empty_index_cache_entry(istate, len);
 
 	ce->ce_mode = create_ce_mode(n->mode);
 	ce->ce_flags = create_ce_flags(stage);
@@ -835,7 +842,13 @@ static int unpack_nondirectories(int n, unsigned long mask,
 			stage = 3;
 		else
 			stage = 2;
-		src[i + o->merge] = create_ce_entry(info, names + i, stage);
+
+		/*
+		 * If this is a merge operation, then the cache
+		 * entries are only temporary and discarded several
+		 * lines below.
+		 */
+		src[i + o->merge] = create_ce_entry(info, names + i, stage, &o->result, o->merge);
 	}
 
 	if (o->merge) {
@@ -844,7 +857,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		for (i = 0; i < n; i++) {
 			struct cache_entry *ce = src[i + o->merge];
 			if (ce != o->df_conflict_entry)
-				free(ce);
+				discard_cache_entry(ce);
 		}
 		return rc;
 	}
@@ -1765,7 +1778,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce);
+	struct cache_entry *merge = dup_entry(ce, &o->result);
 
 	if (!old) {
 		/*
@@ -1785,7 +1798,7 @@ static int merged_entry(const struct cache_entry *ce,
 
 		if (verify_absent(merge,
 				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
-			free(merge);
+			discard_cache_entry(merge);
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
@@ -1811,7 +1824,7 @@ static int merged_entry(const struct cache_entry *ce,
 			update = 0;
 		} else {
 			if (verify_uptodate(old, o)) {
-				free(merge);
+				discard_cache_entry(merge);
 				return -1;
 			}
 			/* Migrate old flags over */
-- 
2.14.3

Re: [PATCH v3 2/7] block alloc: add lifecycle APIs for cache_entry structs

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> Add an API around managing the lifetime of cache_entry
> structs. Abstracting memory management details behind an API will
> allow for alternative memory management strategies without affecting
> all the call sites.  This commit does not change how memory is
> allocated / freed. A later commit in this series will allocate cache
> entries from memory pools as appropriate.
>
> Motivation:
> It has been observed that the time spent loading an index with a large
> number of entries is partly dominated by malloc() calls. This change
> is in preparation for using memory pools to reduce the number of
> malloc() calls made when loading an index.
>
> This API makes a distinction between cache entries that are intended
> for use with a particular index and cache entries that are not. This
> enables us to use the knowledge about how a cache entry will be used
> to make informed decisions about how to handle the corresponding
> memory.

Yuck.  make_index_cache_entry()?

Generally we use "cache" when working on the_index without passing
istate, and otherwise "index", which means that readers can assume
that distim_cache_entry(...)" is a shorter and more limited way to
say "distim_index_entry(&the_index, ...)".  Having both index and
cache in the same name smells crazy.

If most of the alocations are for permanent kind, give it a shorter
name call it make_cache_entry(&the_index, ...), and call the other
non-permanent one with a longer and more cumbersome name, perhaps
make_transient_cache_entry(...).  Avoid saying "index" in the former
name, as the design decision this series is making to allocate
memory for a cache-entry from a pool associated to an index_state is
already seen by what its first parameter is.

> diff --git a/cache.h b/cache.h
> index f0a407602c..204f788438 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -339,6 +339,29 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
>  extern void free_name_hash(struct index_state *istate);
>  
>  
> +/* Cache entry creation and freeing */
> +
> +/*
> + * Create cache_entry intended for use in the specified index. Caller
> + * is responsible for discarding the cache_entry with
> + * `discard_cache_entry`.
> + */
> +extern struct cache_entry *make_index_cache_entry(struct index_state *istate, unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
> +extern struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t name_len);
> +
> +/*
> + * Create a cache_entry that is not intended to be added to an index.
> + * Caller is responsible for discarding the cache_entry
> + * with `discard_cache_entry`.
> + */
> +extern struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage);
> +extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
> +
> +/*
> + * Discard cache entry.
> + */
> +void discard_cache_entry(struct cache_entry *ce);

I am not yet convinced that it is a good idea to require each istate
to hold a separate pool.  Anything that uses unpack_trees() can do
"starting from this src_index, perform various mergy operations and
deposit the result in dst_index".  Sometimes the two logical indices
point at the same istate, sometimes different.  When src and dst are
different istates, the code that used to simply add another pointer
to the same ce to the dst index now needs to duplicate it out of the
pool associated with dst?

In any case, perhaps it will become clearer why it is a good idea as
we read on, so let's do so.

RE: [PATCH v3 2/7] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

> -----Original Message-----
> From: Junio C Hamano <jch2355@gmail.com> On Behalf Of Junio C Hamano
> Sent: Thursday, May 24, 2018 12:52 AM
> To: Jameson Miller <jamill@microsoft.com>
> Cc: git@vger.kernel.org; pclouds@gmail.com; jonathantanmy@google.com;
> sbeller@google.com; peartben@gmail.com
> Subject: Re: [PATCH v3 2/7] block alloc: add lifecycle APIs for cache_entry
> structs
> 
> Jameson Miller <jamill@microsoft.com> writes:
> 
> > Add an API around managing the lifetime of cache_entry structs.
> > Abstracting memory management details behind an API will allow for
> > alternative memory management strategies without affecting all the
> > call sites.  This commit does not change how memory is allocated /
> > freed. A later commit in this series will allocate cache entries from
> > memory pools as appropriate.
> >
> > Motivation:
> > It has been observed that the time spent loading an index with a large
> > number of entries is partly dominated by malloc() calls. This change
> > is in preparation for using memory pools to reduce the number of
> > malloc() calls made when loading an index.
> >
> > This API makes a distinction between cache entries that are intended
> > for use with a particular index and cache entries that are not. This
> > enables us to use the knowledge about how a cache entry will be used
> > to make informed decisions about how to handle the corresponding
> > memory.
> 
> Yuck.  make_index_cache_entry()?
> 
> Generally we use "cache" when working on the_index without passing istate,
> and otherwise "index", which means that readers can assume that
> distim_cache_entry(...)" is a shorter and more limited way to say
> "distim_index_entry(&the_index, ...)".  Having both index and cache in the same
> name smells crazy.
> 
> If most of the alocations are for permanent kind, give it a shorter name call it
> make_cache_entry(&the_index, ...), and call the other non-permanent one with
> a longer and more cumbersome name, perhaps
> make_transient_cache_entry(...).  Avoid saying "index" in the former name, as
> the design decision this series is making to allocate memory for a cache-entry
> from a pool associated to an index_state is already seen by what its first
> parameter is.

I like this suggestion - I will make this change in the next version of this series.

> 
> > diff --git a/cache.h b/cache.h
> > index f0a407602c..204f788438 100644
> > --- a/cache.h
> > +++ b/cache.h
> > @@ -339,6 +339,29 @@ extern void remove_name_hash(struct index_state
> > *istate, struct cache_entry *ce)  extern void free_name_hash(struct
> > index_state *istate);
> >
> >
> > +/* Cache entry creation and freeing */
> > +
> > +/*
> > + * Create cache_entry intended for use in the specified index. Caller
> > + * is responsible for discarding the cache_entry with
> > + * `discard_cache_entry`.
> > + */
> > +extern struct cache_entry *make_index_cache_entry(struct index_state
> > +*istate, unsigned int mode, const unsigned char *sha1, const char
> > +*path, int stage, unsigned int refresh_options); extern struct
> > +cache_entry *make_empty_index_cache_entry(struct index_state *istate,
> > +size_t name_len);
> > +
> > +/*
> > + * Create a cache_entry that is not intended to be added to an index.
> > + * Caller is responsible for discarding the cache_entry
> > + * with `discard_cache_entry`.
> > + */
> > +extern struct cache_entry *make_transient_cache_entry(unsigned int
> > +mode, const unsigned char *sha1, const char *path, int stage); extern
> > +struct cache_entry *make_empty_transient_cache_entry(size_t
> > +name_len);
> > +
> > +/*
> > + * Discard cache entry.
> > + */
> > +void discard_cache_entry(struct cache_entry *ce);
> 
> I am not yet convinced that it is a good idea to require each istate to hold a
> separate pool.  Anything that uses unpack_trees() can do "starting from this
> src_index, perform various mergy operations and deposit the result in
> dst_index".  Sometimes the two logical indices point at the same istate,
> sometimes different.  When src and dst are different istates, the code that used
> to simply add another pointer to the same ce to the dst index now needs to
> duplicate it out of the pool associated with dst?

I did not see any instances in unpack_trees() where it copied
just the cache_entry pointer from src to dst, but I will check
again.

You are correct, all the cache_entries need to be duplicated
before being added to the destination index, which is what I
think the code already does.  We tried to make this more
explicity by converting the inline xcalloc/memcpy instances to an
actual function.

In the existing code (before this patch series), the index
implicitly "owns" its cache_entry instances. This can be seen in
the discard_index function, where the index will discard any
cache entries that it has a reference to (that are not contained
in the split index). If there is code that just copies the
pointer to an unrelated index, then this cache entry would be
freed when the source index is freed (unless the cache entry is
removed from the src index).

With memory pools, the same pattern is followed, but this
relationship is a bit more explicit.

> 
> In any case, perhaps it will become clearer why it is a good idea as we read on,
> so let's do so.

Thank you for your review so far. I look forward to your thoughts on
the overall change and if it is a change you are interested in.

[PATCH v3 3/7] mem-pool: only search head block for available space

[Jameson Miller]

Instead of searching all memory blocks for available space to fulfill
a memory request, only search the head block. If the head block does
not have space, assume that previous block would most likely not be
able to fulfill request either. This could potentially lead to more
memory fragmentation, but also avoids searching memory blocks that
probably will not be able to fulfill request.

This pattern will benefit consumers that are able to generate a good
estimate for how much memory will be needed, or if they are performing
fixed sized allocations, so that once a block is exhausted it will
never be able to fulfill a future request.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index 389d7af447..c80124f1fe 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -21,16 +21,16 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
-	struct mp_block *p;
+	struct mp_block *p = NULL;
 	void *r;
 
 	/* round up to a 'uintmax_t' alignment */
 	if (len & (sizeof(uintmax_t) - 1))
 		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
 
-	for (p = mem_pool->mp_block; p; p = p->next_block)
-		if (p->end - p->next_free >= len)
-			break;
+	if (mem_pool->mp_block &&
+	    mem_pool->mp_block->end - mem_pool->mp_block->next_free >= len)
+		p = mem_pool->mp_block;
 
 	if (!p) {
 		if (len >= (mem_pool->block_alloc / 2)) {
-- 
2.14.3

[PATCH v3 4/7] mem-pool: add lifecycle management functions

[Jameson Miller]

Add initialization and discard functions to mem-pool type. As part of
this, we now also track "large" allocations of memory so that these
can also be cleaned up when discarding the memory pool.

These changes are in preparation for a future commit that will utilize
creating and discarding memory pool.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 fast-import.c |  2 +-
 mem-pool.c    | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 mem-pool.h    | 12 +++++++++++-
 3 files changed, 71 insertions(+), 6 deletions(-)

diff --git a/fast-import.c b/fast-import.c
index 34edf3fb8f..571898e5db 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -300,7 +300,7 @@ static int global_argc;
 static const char **global_argv;
 
 /* Memory pools */
-static struct mem_pool fi_mem_pool =  {NULL, 2*1024*1024 -
+static struct mem_pool fi_mem_pool =  {NULL, NULL, 2*1024*1024 -
 				       sizeof(struct mp_block), 0 };
 
 /* Atom management */
diff --git a/mem-pool.c b/mem-pool.c
index c80124f1fe..01595bcca5 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -5,20 +5,77 @@
 #include "cache.h"
 #include "mem-pool.h"
 
+#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
+
 static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
 {
 	struct mp_block *p;
 
 	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
 	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
+
 	p->next_block = mem_pool->mp_block;
 	p->next_free = (char *)p->space;
 	p->end = p->next_free + block_alloc;
+
 	mem_pool->mp_block = p;
 
+	if (!mem_pool->mp_block_tail)
+		mem_pool->mp_block_tail = p;
+
+	return p;
+}
+
+static void *mem_pool_alloc_custom(struct mem_pool *mem_pool, size_t block_alloc)
+{
+	struct mp_block *p;
+
+	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
+	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
+
+	p->next_block = NULL;
+	p->next_free = (char *)p->space;
+	p->end = p->next_free + block_alloc;
+
+	if (mem_pool->mp_block_tail)
+		mem_pool->mp_block_tail->next_block = p;
+	else
+		mem_pool->mp_block = p;
+
+	mem_pool->mp_block_tail = p;
 	return p;
 }
 
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
+{
+	struct mem_pool *pool;
+
+	if (*mem_pool)
+		return;
+
+	pool = xcalloc(1, sizeof(*pool));
+
+	pool->block_alloc = BLOCK_GROWTH_SIZE;
+
+	if (initial_size > 0)
+		mem_pool_alloc_block(pool, initial_size);
+
+	*mem_pool = pool;
+}
+
+void mem_pool_discard(struct mem_pool *mem_pool)
+{
+	struct mp_block *block, *block_to_free;
+	for (block = mem_pool->mp_block; block;)
+	{
+		block_to_free = block;
+		block = block->next_block;
+		free(block_to_free);
+	}
+
+	free(mem_pool);
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p = NULL;
@@ -33,10 +90,8 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 		p = mem_pool->mp_block;
 
 	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2)) {
-			mem_pool->pool_alloc += len;
-			return xmalloc(len);
-		}
+		if (len >= (mem_pool->block_alloc / 2))
+			return mem_pool_alloc_custom(mem_pool, len);
 
 		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
 	}
diff --git a/mem-pool.h b/mem-pool.h
index 829ad58ecf..5d3e6a367a 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -9,7 +9,7 @@ struct mp_block {
 };
 
 struct mem_pool {
-	struct mp_block *mp_block;
+	struct mp_block *mp_block, *mp_block_tail;
 
 	/*
 	 * The amount of available memory to grow the pool by.
@@ -21,6 +21,16 @@ struct mem_pool {
 	size_t pool_alloc;
 };
 
+/*
+ * Initialize mem_pool with specified initial size.
+ */
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
+
+/*
+ * Discard a memory pool and free all the memory it is responsible for.
+ */
+void mem_pool_discard(struct mem_pool *mem_pool);
+
 /*
  * Alloc memory from the mem_pool.
  */
-- 
2.14.3

[PATCH v3 5/7] mem-pool: fill out functionality

[Jameson Miller]

Add functions for:

    - combining two memory pools

    - determining if a memory address is within the range managed by a
      memory pool

These functions will be used by future commits.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 40 ++++++++++++++++++++++++++++++++++++++++
 mem-pool.h | 13 +++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/mem-pool.c b/mem-pool.c
index 01595bcca5..cc7d3a7ab1 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -108,3 +108,43 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	memset(r, 0, len);
 	return r;
 }
+
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
+{
+	struct mp_block *p;
+
+	/* Check if memory is allocated in a block */
+	for (p = mem_pool->mp_block; p; p = p->next_block)
+		if ((mem >= ((void *)p->space)) &&
+		    (mem < ((void *)p->end)))
+			return 1;
+
+	return 0;
+}
+
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
+{
+	/* Append the blocks from src to dst */
+	if (dst->mp_block && src->mp_block) {
+		/*
+		 * src and dst have blocks, append
+		 * blocks from src to dst.
+		 */
+		dst->mp_block_tail->next_block = src->mp_block;
+		dst->mp_block_tail = src->mp_block_tail;
+	} else if (src->mp_block) {
+		/*
+		 * src has blocks, dst is empty
+		 * use pointers from src to set up dst.
+		 */
+		dst->mp_block = src->mp_block;
+		dst->mp_block_tail = src->mp_block_tail;
+	} else {
+		// src is empty, nothing to do.
+	}
+
+	dst->pool_alloc += src->pool_alloc;
+	src->pool_alloc = 0;
+	src->mp_block = NULL;
+	src->mp_block_tail = NULL;
+}
diff --git a/mem-pool.h b/mem-pool.h
index 5d3e6a367a..5c892d3bdb 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -41,4 +41,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
+ * pool will be empty and not contain any memory. It still needs to be free'd
+ * with a call to `mem_pool_discard`.
+ */
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
+
+/*
+ * Check if a memory pointed at by 'mem' is part of the range of
+ * memory managed by the specified mem_pool.
+ */
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
+
 #endif
-- 
2.14.3

Re: [PATCH v3 5/7] mem-pool: fill out functionality

[Stefan Beller]

> @@ -108,3 +108,43 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
>         memset(r, 0, len);
>         return r;
>  }
> +
> +int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
> +{
> +       struct mp_block *p;
> +
> +       /* Check if memory is allocated in a block */
> +       for (p = mem_pool->mp_block; p; p = p->next_block)
> +               if ((mem >= ((void *)p->space)) &&
> +                   (mem < ((void *)p->end)))
> +                       return 1;
> +
> +       return 0;
> +}
> +
> +void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
> +{
> +       /* Append the blocks from src to dst */
> +       if (dst->mp_block && src->mp_block) {
> +               /*
> +                * src and dst have blocks, append
> +                * blocks from src to dst.
> +                */
> +               dst->mp_block_tail->next_block = src->mp_block;
> +               dst->mp_block_tail = src->mp_block_tail;
> +       } else if (src->mp_block) {
> +               /*
> +                * src has blocks, dst is empty
> +                * use pointers from src to set up dst.
> +                */
> +               dst->mp_block = src->mp_block;
> +               dst->mp_block_tail = src->mp_block_tail;
> +       } else {
> +               // src is empty, nothing to do.

comment style.

[PATCH v3 6/7] block alloc: allocate cache entries from mem_pool

[Jameson Miller]

When reading large indexes from disk, a portion of the time is
dominated in malloc() calls. This can be mitigated by allocating a
large block of memory and manage it ourselves via memory pools.

This change moves the cache entry allocation to be on top of memory
pools.

Design:

The index_state struct will gain a notion of an associated memory_pool
from which cache_entries will be allocated from. When reading in the
index from disk, we have information on the number of entries and
their size, which can guide us in deciding how large our initial
memory allocation should be. When an index is discarded, the
associated memory_pool will be discarded as well - so the lifetime of
a cache_entry is tied to the lifetime of the index_state that it was
allocated for.

In the case of a Split Index, the following rules are followed. 1st,
some terminology is defined:

Terminology:
  - 'the_index': represents the logical view of the index

  - 'split_index': represents the "base" cache entries. Read from the
    split index file.

'the_index' can reference a single split_index, as well as
cache_entries from the split_index. `the_index` will be discarded
before the `split_index` is.  This means that when we are allocating
cache_entries in the presence of a split index, we need to allocate
the entries from the `split_index`'s memory pool.  This allows us to
follow the pattern that `the_index` can reference cache_entries from
the `split_index`, and that the cache_entries will not be freed while
they are still being referenced.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h        |  21 ++++++++++
 read-cache.c   | 119 ++++++++++++++++++++++++++++++++++++++++++++++++---------
 split-index.c  |  50 ++++++++++++++++++++----
 unpack-trees.c |  13 +------
 4 files changed, 165 insertions(+), 38 deletions(-)

diff --git a/cache.h b/cache.h
index 204f788438..7aae9c8db0 100644
--- a/cache.h
+++ b/cache.h
@@ -15,6 +15,7 @@
 #include "path.h"
 #include "sha1-array.h"
 #include "repository.h"
+#include "mem-pool.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -156,6 +157,7 @@ struct cache_entry {
 	struct stat_data ce_stat_data;
 	unsigned int ce_mode;
 	unsigned int ce_flags;
+	unsigned int mem_pool_allocated;
 	unsigned int ce_namelen;
 	unsigned int index;	/* for link extension */
 	struct object_id oid;
@@ -227,6 +229,7 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 				    const struct cache_entry *src)
 {
 	unsigned int state = dst->ce_flags & CE_HASHED;
+	int mem_pool_allocated = dst->mem_pool_allocated;
 
 	/* Don't copy hash chain and name */
 	memcpy(&dst->ce_stat_data, &src->ce_stat_data,
@@ -235,6 +238,9 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 
 	/* Restore the hash state */
 	dst->ce_flags = (dst->ce_flags & ~CE_HASHED) | state;
+
+	/* Restore the mem_pool_allocated flag */
+	dst->mem_pool_allocated = mem_pool_allocated;
 }
 
 static inline unsigned create_ce_flags(unsigned stage)
@@ -328,6 +334,7 @@ struct index_state {
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
+	struct mem_pool *ce_mem_pool;
 };
 
 extern struct index_state the_index;
@@ -362,6 +369,20 @@ extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Duplicate a cache_entry. Allocate memory for the new entry from a
+ * memory_pool. Takes into account cache_entry fields that are meant
+ * for managing the underlying memory allocation of the cache_entry.
+ */
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce, struct index_state *istate);
+
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/read-cache.c b/read-cache.c
index d51cc83312..02fe5d333c 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -46,6 +46,48 @@
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
 		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
+
+/*
+ * This is an estimate of the pathname length in the index.  We use
+ * this for V4 index files to guess the un-deltafied size of the index
+ * in memory because of pathname deltafication.  This is not required
+ * for V2/V3 index formats because their pathnames are not compressed.
+ * If the initial amount of memory set aside is not sufficient, the
+ * mem pool will allocate extra memory.
+ */
+#define CACHE_ENTRY_PATH_LENGTH 80
+
+static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry *ce;
+	ce = mem_pool_alloc(mem_pool, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry * ce;
+	ce = mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static struct mem_pool *find_mem_pool(struct index_state *istate)
+{
+	struct mem_pool **pool_ptr;
+
+	if (istate->split_index && istate->split_index->base)
+		pool_ptr = &istate->split_index->base->ce_mem_pool;
+	else
+		pool_ptr = &istate->ce_mem_pool;
+
+	if (!*pool_ptr)
+		mem_pool_init(pool_ptr, 0);
+
+	return *pool_ptr;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -746,7 +788,7 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 
 struct cache_entry *make_empty_index_cache_entry(struct index_state *istate, size_t len)
 {
-	return xcalloc(1, cache_entry_size(len));
+	return mem_pool__ce_calloc(find_mem_pool(istate), len);
 }
 
 struct cache_entry *make_empty_transient_cache_entry(size_t len)
@@ -1641,13 +1683,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+static struct cache_entry *cache_entry_from_ondisk(struct mem_pool *mem_pool,
 						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = make_empty_index_cache_entry(istate, len);
+	struct cache_entry *ce = mem_pool__ce_alloc(mem_pool, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1689,7 +1731,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct index_state *istate,
+static struct cache_entry *create_from_disk(struct mem_pool *mem_pool,
 					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
@@ -1721,13 +1763,13 @@ static struct cache_entry *create_from_disk(struct index_state *istate,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags,
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1801,6 +1843,22 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_fsmonitor(istate);
 }
 
+static size_t estimate_cache_size_from_compressed(unsigned int entries)
+{
+	return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_PATH_LENGTH);
+}
+
+static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
+{
+	long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
+
+	/*
+	 * Account for potential alignment differences.
+	 */
+	per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	return ondisk_size + entries * per_entry;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1847,10 +1905,15 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
 	istate->initialized = 1;
 
-	if (istate->version == 4)
+	if (istate->version == 4) {
 		previous_name = &previous_name_buf;
-	else
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size_from_compressed(istate->cache_nr));
+	} else {
 		previous_name = NULL;
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size(mmap_size, istate->cache_nr));
+	}
 
 	src_offset = sizeof(*hdr);
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -1859,7 +1922,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate->ce_mem_pool, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1956,17 +2019,13 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-	int i;
+	/*
+	 * Cache entries in istate->cache[] should have been allocated
+	 * from the memory pool associated with this index, or from an
+	 * associated split_index. There is no need to free individual
+	 * cache entries.
+	 */
 
-	for (i = 0; i < istate->cache_nr; i++) {
-		if (istate->cache[i]->index &&
-		    istate->split_index &&
-		    istate->split_index->base &&
-		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-			continue;
-		discard_cache_entry(istate->cache[i]);
-	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -1980,6 +2039,12 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool);
+		istate->ce_mem_pool = NULL;
+	}
+
 	return 0;
 }
 
@@ -2771,10 +2836,26 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	src->untracked = NULL;
 }
 
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
+		     struct index_state *istate)
+{
+	unsigned int size = ce_size(ce);
+	int mem_pool_allocated;
+	struct cache_entry *new_entry = make_empty_index_cache_entry(istate, ce_namelen(ce));
+	mem_pool_allocated = new_entry->mem_pool_allocated;
+
+	memcpy(new_entry, ce, size);
+	new_entry->mem_pool_allocated = mem_pool_allocated;
+	return new_entry;
+}
+
 /*
  * Free cache entry.
  */
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && ce->mem_pool_allocated)
+		return;
+
 	free(ce);
 }
diff --git a/split-index.c b/split-index.c
index ab638b844d..004d785d2f 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,16 +73,31 @@ void move_cache_to_base_index(struct index_state *istate)
 	int i;
 
 	/*
-	 * do not delete old si->base, its index entries may be shared
-	 * with istate->cache[]. Accept a bit of leaking here because
-	 * this code is only used by short-lived update-index.
+	 * If there was a previous base index, then transfer ownership of allocated
+	 * entries to the parent index.
 	 */
+	if (si->base &&
+		si->base->ce_mem_pool) {
+
+		if (!istate->ce_mem_pool)
+			mem_pool_init(&istate->ce_mem_pool, 0);
+
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+	}
+
 	si->base = xcalloc(1, sizeof(*si->base));
 	si->base->version = istate->version;
 	/* zero timestamp disables racy test in ce_write_index() */
 	si->base->timestamp = istate->timestamp;
 	ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
 	si->base->cache_nr = istate->cache_nr;
+
+	/*
+	 * The mem_pool needs to move with the allocated entries.
+	 */
+	si->base->ce_mem_pool = istate->ce_mem_pool;
+	istate->ce_mem_pool = NULL;
+
 	COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
 	mark_base_index_entries(si->base);
 	for (i = 0; i < si->base->cache_nr; i++)
@@ -331,12 +346,31 @@ void remove_split_index(struct index_state *istate)
 {
 	if (istate->split_index) {
 		/*
-		 * can't discard_split_index(&the_index); because that
-		 * will destroy split_index->base->cache[], which may
-		 * be shared with the_index.cache[]. So yeah we're
-		 * leaking a bit here.
+		 * When removing the split index, we need to move
+		 * ownership of the mem_pool associated with the
+		 * base index to the main index. There may be cache entries
+		 * allocated from the base's memory pool that are shared with
+		 * the_index.cache[].
 		 */
-		istate->split_index = NULL;
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+
+		/*
+		 * The split index no longer owns the mem_pool backing
+		 * its cache array. As we are discarding this index,
+		 * mark the index as having no cache entries, so it
+		 * will not attempt to clean up the cache entries or
+		 * validate them.
+		 */
+		if (istate->split_index->base)
+			istate->split_index->base->cache_nr = 0;
+
+		/*
+		 * We can discard the split index because its
+		 * memory pool has been incorporated into the
+		 * memory pool associated with the the_index.
+		 */
+		discard_split_index(istate);
+
 		istate->cache_changed |= SOMETHING_CHANGED;
 	}
 }
diff --git a/unpack-trees.c b/unpack-trees.c
index dd4d12ba45..dc53f811ae 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -192,20 +192,11 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
-{
-	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = make_empty_index_cache_entry(istate, ce_namelen(ce));
-
-	memcpy(new_entry, ce, size);
-	return new_entry;
-}
-
 static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
+	do_add_entry(o, dup_cache_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -1778,7 +1769,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce, &o->result);
+	struct cache_entry *merge = dup_cache_entry(ce, &o->result);
 
 	if (!old) {
 		/*
-- 
2.14.3

[PATCH v3 7/7] block alloc: add validations around cache_entry lifecyle

[Jameson Miller]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h      |  6 ++++++
 git.c        |  3 +++
 mem-pool.c   |  7 ++++++-
 mem-pool.h   |  2 +-
 read-cache.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 5 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/cache.h b/cache.h
index 7aae9c8db0..2916e953ad 100644
--- a/cache.h
+++ b/cache.h
@@ -369,6 +369,12 @@ extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Check configuration if we should perform extra validation on cache
+ * entries.
+ */
+int should_validate_cache_entries(void);
+
 /*
  * Duplicate a cache_entry. Allocate memory for the new entry from a
  * memory_pool. Takes into account cache_entry fields that are meant
diff --git a/git.c b/git.c
index bab6bbfded..7ce65eab78 100644
--- a/git.c
+++ b/git.c
@@ -347,7 +347,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index cc7d3a7ab1..6770b4f740 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -63,13 +63,18 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
 	*mem_pool = pool;
 }
 
-void mem_pool_discard(struct mem_pool *mem_pool)
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory)
 {
 	struct mp_block *block, *block_to_free;
+
 	for (block = mem_pool->mp_block; block;)
 	{
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
diff --git a/mem-pool.h b/mem-pool.h
index 5c892d3bdb..68d8428902 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -29,7 +29,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
 /*
  * Discard a memory pool and free all the memory it is responsible for.
  */
-void mem_pool_discard(struct mem_pool *mem_pool);
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory);
 
 /*
  * Alloc memory from the mem_pool.
diff --git a/read-cache.c b/read-cache.c
index 02fe5d333c..fb2cec6ac6 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2023,8 +2023,10 @@ int discard_index(struct index_state *istate)
 	 * Cache entries in istate->cache[] should have been allocated
 	 * from the memory pool associated with this index, or from an
 	 * associated split_index. There is no need to free individual
-	 * cache entries.
+	 * cache entries. validate_cache_entries can detect when this
+	 * assertion does not hold.
 	 */
+	validate_cache_entries(istate);
 
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2041,13 +2043,45 @@ int discard_index(struct index_state *istate)
 	istate->untracked = NULL;
 
 	if (istate->ce_mem_pool) {
-		mem_pool_discard(istate->ce_mem_pool);
+		mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
 		istate->ce_mem_pool = NULL;
 	}
 
 	return 0;
 }
 
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+
+	if (!should_validate_cache_entries() ||!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2854,8 +2888,25 @@ struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
  */
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && should_validate_cache_entries())
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
+
 	if (ce && ce->mem_pool_allocated)
 		return;
 
 	free(ce);
 }
+
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
-- 
2.14.3

Re: [PATCH v3 0/7] allocate cache entries from memory pool

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> Changes from V2:
>
> 	- Tweak logic of finding available memory block for memory
>           allocation
> 	
> 	  - Only search head block

Hmph.  Is that because we generally do not free() a lot so once a
block is filled, there is not much chance that we have reclaimed
space in the block later?

> 	- Tweaked handling of large memory allocations.
> 	
> 	  - Large blocks now tracked in same manner as "regular"
>             blocks
> 	  
> 	  - Large blocks are placed at end of linked list of memory
>             blocks

If we are only carving out of the most recently allocated block, it
seems that there is no point looking for "the end", no?


> 	- Cache_entry type gains notion of whether it was allocated
>           from memory pool or not
> 	
> 	  - Collapsed cache_entry discard logic into single
>             function. This should make code easier to maintain

That certainly should be safer to have a back-pointer pointing to
which pool each entry came from, but doesn't it result in memory
bloat?

RE: [PATCH v3 0/7] allocate cache entries from memory pool

[Jameson Miller]

> -----Original Message-----
> From: Junio C Hamano <jch2355@gmail.com> On Behalf Of Junio C Hamano
> Sent: Thursday, May 24, 2018 12:55 AM
> To: Jameson Miller <jamill@microsoft.com>
> Cc: git@vger.kernel.org; pclouds@gmail.com; jonathantanmy@google.com;
> sbeller@google.com; peartben@gmail.com
> Subject: Re: [PATCH v3 0/7] allocate cache entries from memory pool
> 
> Jameson Miller <jamill@microsoft.com> writes:
> 
> > Changes from V2:
> >
> > 	- Tweak logic of finding available memory block for memory
> >           allocation
> >
> > 	  - Only search head block
> 
> Hmph.  Is that because we generally do not free() a lot so once a block is filled,
> there is not much chance that we have reclaimed space in the block later?
> 

The design of the memory pool is that once the memory is
claimed from the pool, it is not reused until the
containing pool is discarded. Individual entries are not
freed, only the entire memory pool is freed, and only after we
are sure that there are no references to any of the entries in the
pool.

The memory pool design makes some tradeoffs. It is not meant to
be completely replace malloc / free as a general purpose
allocator, but rather used in scenarios where the benefit (faster
allocations, lower bookkeeping overhead) is worth the
tradeoffs (not able to free individual allocations). The access
patterns around cache entries are well matched with the memory
pool to get the benefits - the majority of cache entries are
allocated up front when reading the index from disk, and are then
discarded in bulk when the index is freed (if the index is freed
at all (rather than just existing)).

> > 	- Tweaked handling of large memory allocations.
> >
> > 	  - Large blocks now tracked in same manner as "regular"
> >             blocks
> >
> > 	  - Large blocks are placed at end of linked list of memory
> >             blocks
> 
> If we are only carving out of the most recently allocated block, it seems that
> there is no point looking for "the end", no?

Right. If we are not searching the list, then there isn't any point in
Appending odd large items to the end vs sticking it immediately past
the head block. I will remove the usage of the tail pointer in the
next version.

Yes, this is true. I can remove the usage of the tail pointer here,
as it is not really leveraged. I will make this change in the next version.

> 
> 
> > 	- Cache_entry type gains notion of whether it was allocated
> >           from memory pool or not
> >
> > 	  - Collapsed cache_entry discard logic into single
> >             function. This should make code easier to maintain
> 
> That certainly should be safer to have a back-pointer pointing to which pool
> each entry came from, but doesn't it result in memory bloat?

Currently, entries claimed from a memory pool are not freed, so we only need
to know whether the entry came from a memory pool or not. This has less memory 
impact than a full pointer but is also a bit more restrictive.

We debated several approaches for what to do here and landed on using a simple bit
for this rather than the full pointer. In the current code we use a full integer field for this, but
we can convert this into a bit or bit field. The current flags word is full, so this would require
a second flags field.

Re: [PATCH v3 0/7] allocate cache entries from memory pool

[Stefan Beller]

>
> The memory pool design makes some tradeoffs. It is not meant to
> be completely replace malloc / free as a general purpose
> allocator, but rather used in scenarios where the benefit (faster
> allocations, lower bookkeeping overhead) is worth the
> tradeoffs (not able to free individual allocations).

So this is the actual stated design goal of this memory pool?
Fast&cheap allocation with little overhead for giving up individual frees?

> We debated several approaches for what to do here

it would be awesome if the list could participate in the discussion
even if only read-only.

RE: [PATCH v3 0/7] allocate cache entries from memory pool

[Jameson Miller]

> 
> > We debated several approaches for what to do here
> 
> it would be awesome if the list could participate in the discussion even if only
> read-only.

A bit of delay in my response here, but I like the suggestion. here is a summary of
some approaches I considered:

1) Do not include any information about where the cache_entry was allocated.
     Pros: No extra memory overhead
     Cons: Caller is responsible for freeing the cache entry correctly

This was our initial approach. We were hoping that all cache
entries could be allocated from a memory pool, and we would not
have to worry about non-pool allocated entries. There are still a
couple of places that need "temporary" cache entries at the
moment, so we couldn't move completely to only memory pool
allocated cache_entries. This would have resulted in the code
allocating many "temporary" cache_entries from a pool, and the
memory would not be eligible to be reclaimed until the entire
memory pool was freed - and this was a tradeoff we didn't want to
make.

2) Include an extra field encoding whether the cache_entry was
   allocated from a memory pool

    Pro: the discard function can now make a decision regarding how
         to free the cache_entry
    Con: each cache entry grows by an extra int field.

The bits in the existing ce_flags field are all claimed, so we
need an extra field to track this bit of information. We could
claim just a bit in the field now, which would result in the
cache_entry still growing by the same amount, but any future bits
would not require extra space. This pushes off the work for an
actual bit field off into future work.

3) Encode whether the cache_entry was allocated from a memory
   pool as a bit in a field.

    Pro: only a single bit is required to encode this information.
    Con: All the existings bits in the existing ce_flags field are
         claimed. We need to add an extra bit field and take the same
         memory growth.

I considered this approach (and am still open to it), but I went
for a simpler initial approach to make sure the overall change is
acceptable. There is no difference in the memory footprint with
this change, so it is only to enable future changes more easily.

4) Include pointer to the memory pool from which this cache_entry
   was created from

    Pro: Could (potentially) do some extra bookkeeping, such as
         automatically cleaning up the memory_pool when all
         allocated cache_entries are freed.
    Con: extra complexity, larger growth to cache_entry struct to
         accommodate mem_pool pointer

In the end, we didn't see a tangible benefit to this option at this point.

Given the tradeoffs, I went with option #2 for now.

Re: [PATCH v3 0/7] allocate cache entries from memory pool

[Stefan Beller]

On Wed, May 23, 2018 at 7:47 AM, Jameson Miller <jamill@microsoft.com> wrote:
> Changes from V2:
>
>         - Tweak logic of finding available memory block for memory
>           allocation
>
>           - Only search head block
>
>         - Tweaked handling of large memory allocations.
>
>           - Large blocks now tracked in same manner as "regular"
>             blocks
>
>           - Large blocks are placed at end of linked list of memory
>             blocks
>
>         - Cache_entry type gains notion of whether it was allocated
>           from memory pool or not
>
>           - Collapsed cache_entry discard logic into single
>             function. This should make code easier to maintain
>
>         - Small tweaks based on V1 feedback
>
> Base Ref: master
> Web-Diff: git@github.com:jamill/git.git/commit/d608515f9e

Unrelated to this series, but to the tool you use to generate the cover-letter:
I think the Web-Diff only works when you give the http[s] address, git@
won't work here?

[PATCH v4 0/8] Allocate cache entries from mem_pool

[Jameson Miller]

Changes from V3:

Mainly changes from last round of feedback:

  - Rename make_index_cache_entry -> make_cache_entry

  - Rename make_empty_index_cache_entry -> make_empty-cache_entry

  - Remove tail pointer in mem_pool

  - Small code tweaks

  - More accurately calculate mp_block size for platforms that do not
    support flexible arrays


One thing that came up with my testing is that the current automated
tests do not fully cover the code path of "large" allocations from a
memory pool. I was able to force this condition by manually tweaking
some variables and then running the automated tests, but this is not
ideal for preventing regressions in the future.

One way I can think of testing this is to add a test-helper and
directly test the memory pool struct. This will allow me to control
the parameters and different conditions. I was hoping for some
guidance before I actually implemented these tests.

Either way, I would like to do the additional tests in a separate
patch series to have a more focused discussion. I am not sure if these
tests would prevent inclusion of this patch series - I am open to
guidance here.

Base Ref: master
Web-Diff: https://github.com/jamill/git/compare/242ba98e44...667b8de06c

Jameson Miller (8):
  read-cache: teach refresh_cache_entry() to take istate
  block alloc: add lifecycle APIs for cache_entry structs
  mem-pool: only search head block for available space
  mem-pool: tweak math on mp_block allocation size
  mem-pool: add lifecycle management functions
  mem-pool: fill out functionality
  block alloc: allocate cache entries from mem_pool
  block alloc: add validations around cache_entry lifecyle

 apply.c                |  24 +++--
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   6 +-
 builtin/reset.c        |   2 +-
 builtin/update-index.c |  26 +++--
 cache.h                |  53 +++++++++-
 git.c                  |   3 +
 mem-pool.c             | 124 +++++++++++++++++++----
 mem-pool.h             |  23 +++++
 merge-recursive.c      |   4 +-
 read-cache.c           | 259 ++++++++++++++++++++++++++++++++++++++++---------
 resolve-undo.c         |   4 +-
 split-index.c          |  58 ++++++++---
 tree.c                 |   4 +-
 unpack-trees.c         |  40 ++++----
 16 files changed, 504 insertions(+), 139 deletions(-)


base-commit: 242ba98e44d8314fb184d240939614a3c9b424db
-- 
2.14.3

[PATCH v4 1/8] read-cache: teach refresh_cache_entry() to take istate

[Jameson Miller]

Refactor refresh_cache_entry() to work on a specific index, instead of
implicitly using the_index. This is in preparation for making the
make_cache_entry function apply to a specific index.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h           | 2 +-
 merge-recursive.c | 2 +-
 read-cache.c      | 9 +++++----
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/cache.h b/cache.h
index 89a107a7f7..9538511d9f 100644
--- a/cache.h
+++ b/cache.h
@@ -751,7 +751,7 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 #define REFRESH_IGNORE_SUBMODULES	0x0010	/* ignore submodules */
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
-extern struct cache_entry *refresh_cache_entry(struct cache_entry *, unsigned int);
+extern struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 /*
  * Opportunistically update the index but do not complain if we can't.
diff --git a/merge-recursive.c b/merge-recursive.c
index f110e1c5ec..11a767cc72 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -323,7 +323,7 @@ static int add_cacheinfo(struct merge_options *o,
 	if (refresh) {
 		struct cache_entry *nce;
 
-		nce = refresh_cache_entry(ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		nce = refresh_cache_entry(&the_index, ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
 		if (!nce)
 			return err(o, _("add_cacheinfo failed to refresh for path '%s'; merge aborting."), path);
 		if (nce != ce)
diff --git a/read-cache.c b/read-cache.c
index 372588260e..fa8366ecab 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -767,7 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	ce->ce_namelen = len;
 	ce->ce_mode = create_ce_mode(mode);
 
-	ret = refresh_cache_entry(ce, refresh_options);
+	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
 		free(ce);
 	return ret;
@@ -1473,10 +1473,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	return has_errors;
 }
 
-struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
-					       unsigned int options)
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+					struct cache_entry *ce,
+					unsigned int options)
 {
-	return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
-- 
2.14.3

[PATCH v4 2/8] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

Add an API around managing the lifetime of cache_entry
structs. Abstracting memory management details behind this API will
allow for alternative memory management strategies without affecting
all the call sites.  This commit does not change how memory is
allocated or freed. A later commit in this series will allocate cache
entries from memory pools as appropriate.

Motivation:
It has been observed that the time spent loading an index with a large
number of entries is partly dominated by malloc() calls. This change
is in preparation for using memory pools to reduce the number of
malloc() calls made when loading an index.

This API makes a distinction between cache entries that are intended
for use with a particular index and cache entries that are not. This
enables us to use the knowledge about how a cache entry will be used
to make informed decisions about how to handle the corresponding
memory.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 apply.c                | 24 ++++++-------
 blame.c                |  5 ++-
 builtin/checkout.c     |  8 ++---
 builtin/difftool.c     |  6 ++--
 builtin/reset.c        |  2 +-
 builtin/update-index.c | 26 ++++++--------
 cache.h                | 24 ++++++++++++-
 merge-recursive.c      |  2 +-
 read-cache.c           | 96 ++++++++++++++++++++++++++++++++++----------------
 resolve-undo.c         |  4 ++-
 split-index.c          |  8 ++---
 tree.c                 |  4 +--
 unpack-trees.c         | 35 ++++++++++++------
 13 files changed, 155 insertions(+), 89 deletions(-)

diff --git a/apply.c b/apply.c
index d79e61591b..1b5d923f4e 100644
--- a/apply.c
+++ b/apply.c
@@ -4090,12 +4090,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
+		ce = make_cache_entry(&result, patch->old_mode, oid.hash, name, 0, 0);
 		if (!ce)
 			return error(_("make_cache_entry failed for path '%s'"),
 				     name);
 		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("could not add %s to temporary index"),
 				     name);
 		}
@@ -4263,12 +4263,11 @@ static int add_index_file(struct apply_state *state,
 	struct stat st;
 	struct cache_entry *ce;
 	int namelen = strlen(path);
-	unsigned ce_size = cache_entry_size(namelen);
 
 	if (!state->update_index)
 		return 0;
 
-	ce = xcalloc(1, ce_size);
+	ce = make_empty_cache_entry(&the_index, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(0);
@@ -4278,13 +4277,13 @@ static int add_index_file(struct apply_state *state,
 
 		if (!skip_prefix(buf, "Subproject commit ", &s) ||
 		    get_oid_hex(s, &ce->oid)) {
-			free(ce);
-		       return error(_("corrupt patch for submodule %s"), path);
+			discard_cache_entry(ce);
+			return error(_("corrupt patch for submodule %s"), path);
 		}
 	} else {
 		if (!state->cached) {
 			if (lstat(path, &st) < 0) {
-				free(ce);
+				discard_cache_entry(ce);
 				return error_errno(_("unable to stat newly "
 						     "created file '%s'"),
 						   path);
@@ -4292,13 +4291,13 @@ static int add_index_file(struct apply_state *state,
 			fill_stat_cache_info(ce, &st);
 		}
 		if (write_object_file(buf, size, blob_type, &ce->oid) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to create backing store "
 				       "for newly created file %s"), path);
 		}
 	}
 	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error(_("unable to add cache entry for %s"), path);
 	}
 
@@ -4422,27 +4421,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
 				       struct patch *patch)
 {
 	int stage, namelen;
-	unsigned ce_size, mode;
+	unsigned mode;
 	struct cache_entry *ce;
 
 	if (!state->update_index)
 		return 0;
 	namelen = strlen(patch->new_name);
-	ce_size = cache_entry_size(namelen);
 	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
 
 	remove_file_from_cache(patch->new_name);
 	for (stage = 1; stage < 4; stage++) {
 		if (is_null_oid(&patch->threeway_stage[stage - 1]))
 			continue;
-		ce = xcalloc(1, ce_size);
+		ce = make_empty_cache_entry(&the_index, namelen);
 		memcpy(ce->name, patch->new_name, namelen);
 		ce->ce_mode = create_ce_mode(mode);
 		ce->ce_flags = create_ce_flags(stage);
 		ce->ce_namelen = namelen;
 		oidcpy(&ce->oid, &patch->threeway_stage[stage - 1]);
 		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to add cache entry for %s"),
 				     patch->new_name);
 		}
diff --git a/blame.c b/blame.c
index 14d0e0b575..4c6668d0e1 100644
--- a/blame.c
+++ b/blame.c
@@ -154,7 +154,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
 	time_t now;
-	int size, len;
+	int len;
 	struct cache_entry *ce;
 	unsigned mode;
 	struct strbuf msg = STRBUF_INIT;
@@ -252,8 +252,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 			/* Let's not bother reading from HEAD tree */
 			mode = S_IFREG | 0644;
 	}
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, &origin->blob_oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 2e1d2376d2..e44755c371 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -77,7 +77,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -96,7 +96,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		if (ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
@@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_transient_cache_entry(mode, oid.hash, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	discard_cache_entry(ce);
 	return status;
 }
 
diff --git a/builtin/difftool.c b/builtin/difftool.c
index bc97d4aef2..a35d2d4e08 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,10 +321,10 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ce = make_transient_cache_entry(mode, oid->hash, path, 0);
 	ret = checkout_entry(ce, state, NULL);
 
-	free(ce);
+	discard_cache_entry(ce);
 	return ret;
 }
 
@@ -488,7 +488,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
+					make_cache_entry(&wtindex, rmode, roid.hash,
 							 dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
diff --git a/builtin/reset.c b/builtin/reset.c
index a862c70fab..0ea0a19d5e 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,7 +134,7 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, one->oid.hash, one->path,
+		ce = make_cache_entry(&the_index, one->mode, one->oid.hash, one->path,
 				      0, 0);
 		if (!ce)
 			die(_("make_cache_entry failed for path '%s'"),
diff --git a/builtin/update-index.c b/builtin/update-index.c
index a8709a26ec..ea2f2a476c 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -268,15 +268,14 @@ static int process_lstat_error(const char *path, int err)
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
-	int option, size;
+	int option;
 	struct cache_entry *ce;
 
 	/* Was the old index entry already up-to-date? */
 	if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
 		return 0;
 
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
@@ -285,13 +284,13 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 
 	if (index_path(&ce->oid, path, st,
 		       info_only ? 0 : HASH_WRITE_OBJECT)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return -1;
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
 	if (add_cache_entry(ce, option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
 	}
 	return 0;
@@ -402,15 +401,14 @@ static int process_path(const char *path, struct stat *st, int stat_errno)
 static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 			 const char *path, int stage)
 {
-	int size, len, option;
+	int len, option;
 	struct cache_entry *ce;
 
 	if (!verify_path(path, mode))
 		return error("Invalid path '%s'", path);
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -599,7 +597,6 @@ static struct cache_entry *read_one_ent(const char *which,
 {
 	unsigned mode;
 	struct object_id oid;
-	int size;
 	struct cache_entry *ce;
 
 	if (get_tree_entry(ent, path, &oid, &mode)) {
@@ -612,8 +609,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, namelen);
 
 	oidcpy(&ce->oid, &oid);
 	memcpy(ce->name, path, namelen);
@@ -690,8 +686,8 @@ static int unresolve_one(const char *path)
 	error("%s: cannot add their version to the index.", path);
 	ret = -1;
  free_return:
-	free(ce_2);
-	free(ce_3);
+	discard_cache_entry(ce_2);
+	discard_cache_entry(ce_3);
 	return ret;
 }
 
@@ -758,7 +754,7 @@ static int do_reupdate(int ac, const char **av,
 					   ce->name, ce_namelen(ce), 0);
 		if (old && ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
-			free(old);
+			discard_cache_entry(old);
 			continue; /* unchanged */
 		}
 		/* Be careful.  The working tree may not have the
@@ -769,7 +765,7 @@ static int do_reupdate(int ac, const char **av,
 		path = xstrdup(ce->name);
 		update_one(path);
 		free(path);
-		free(old);
+		discard_cache_entry(old);
 		if (save_nr != active_nr)
 			goto redo;
 	}
diff --git a/cache.h b/cache.h
index 9538511d9f..abcc27ff87 100644
--- a/cache.h
+++ b/cache.h
@@ -339,6 +339,29 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 extern void free_name_hash(struct index_state *istate);
 
 
+/* Cache entry creation and cleanup */
+
+/*
+ * Create cache_entry intended for use in the specified index. Caller
+ * is responsible for discarding the cache_entry with
+ * `discard_cache_entry`.
+ */
+extern struct cache_entry *make_cache_entry(struct index_state *istate, unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
+extern struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t name_len);
+
+/*
+ * Create a cache_entry that is not intended to be added to an index.
+ * Caller is responsible for discarding the cache_entry
+ * with `discard_cache_entry`.
+ */
+extern struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage);
+extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
+
+/*
+ * Discard cache entry.
+ */
+void discard_cache_entry(struct cache_entry *ce);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
@@ -698,7 +721,6 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 11a767cc72..330958eb68 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -315,7 +315,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid->hash : null_sha1, path, stage, 0);
+	ce = make_cache_entry(&the_index, mode, oid ? oid->hash : null_sha1, path, stage, 0);
 	if (!ce)
 		return err(o, _("add_cacheinfo failed for path '%s'; merge aborting."), path);
 
diff --git a/read-cache.c b/read-cache.c
index fa8366ecab..6396e04e45 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -61,7 +61,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 	replace_index_entry_in_base(istate, old, ce);
 	remove_name_hash(istate, old);
-	free(old);
+	discard_cache_entry(old);
 	ce->ce_flags &= ~CE_HASHED;
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +74,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new_entry = xmalloc(cache_entry_size(namelen));
+	new_entry = make_empty_cache_entry(istate, namelen);
 	copy_cache_entry(new_entry, old_entry);
 	new_entry->ce_flags &= ~CE_HASHED;
 	new_entry->ce_namelen = namelen;
@@ -623,7 +623,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new_entry = xcalloc(1, cache_entry_size(len));
+	new_entry = make_empty_cache_entry(istate, len);
 	memcpy(new_entry->name, alias->name, len);
 	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
@@ -640,7 +640,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-	int size, namelen, was_same;
+	int namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
@@ -662,8 +662,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_namelen = namelen;
 	if (!intent_only)
@@ -704,13 +703,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 				ce_mark_uptodate(alias);
 			alias->ce_flags |= CE_ADDED;
 
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
 	if (!intent_only) {
 		if (index_path(&ce->oid, path, st, newflags)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error("unable to index file %s", path);
 		}
 	} else
@@ -727,9 +726,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		    ce->ce_mode == alias->ce_mode);
 
 	if (pretend)
-		free(ce);
+		discard_cache_entry(ce);
 	else if (add_index_entry(istate, ce, add_option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("unable to add %s to index", path);
 	}
 	if (verbose && !was_same)
@@ -745,12 +744,22 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 	return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
-		const unsigned char *sha1, const char *path, int stage,
-		unsigned int refresh_options)
+struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_empty_transient_cache_entry(size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_cache_entry(struct index_state *istate, unsigned int mode,
+				     const unsigned char *sha1, const char *path,
+				     int stage, unsigned int refresh_options)
 {
-	int size, len;
 	struct cache_entry *ce, *ret;
+	int len;
 
 	if (!verify_path(path, mode)) {
 		error("Invalid path '%s'", path);
@@ -758,8 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	}
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, len);
 
 	hashcpy(ce->oid.hash, sha1);
 	memcpy(ce->name, path, len);
@@ -769,10 +777,33 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 
 	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
-		free(ce);
+		discard_cache_entry(ce);
 	return ret;
 }
 
+struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1,
+					       const char *path, int stage)
+{
+	struct cache_entry *ce;
+	int len;
+
+	if (!verify_path(path, mode)) {
+		error("Invalid path '%s'", path);
+		return NULL;
+	}
+
+	len = strlen(path);
+	ce = make_empty_transient_cache_entry(len);
+
+	hashcpy(ce->oid.hash, sha1);
+	memcpy(ce->name, path, len);
+	ce->ce_flags = create_ce_flags(stage);
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	return ce;
+}
+
 /*
  * Chmod an index entry with either +x or -x.
  *
@@ -1268,7 +1299,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
 	struct stat st;
 	struct cache_entry *updated;
-	int changed, size;
+	int changed;
 	int refresh = options & CE_MATCH_REFRESH;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
@@ -1348,8 +1379,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
-	size = ce_size(ce);
-	updated = xmalloc(size);
+	updated = make_empty_cache_entry(istate, ce_namelen(ce));
 	copy_cache_entry(updated, ce);
 	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
 	fill_stat_cache_info(updated, &st);
@@ -1635,12 +1665,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = xmalloc(cache_entry_size(len));
+	struct cache_entry *ce = make_empty_cache_entry(istate, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1682,7 +1713,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *create_from_disk(struct index_state *istate,
+					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
 {
@@ -1713,13 +1745,13 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(ondisk, flags,
+		ce = cache_entry_from_ondisk(istate, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1851,7 +1883,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1957,7 +1989,7 @@ int discard_index(struct index_state *istate)
 		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
 		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
 			continue;
-		free(istate->cache[i]);
+		discard_cache_entry(istate->cache[i]);
 	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2647,14 +2679,13 @@ int read_index_unmerged(struct index_state *istate)
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i];
 		struct cache_entry *new_ce;
-		int size, len;
+		int len;
 
 		if (!ce_stage(ce))
 			continue;
 		unmerged = 1;
 		len = ce_namelen(ce);
-		size = cache_entry_size(len);
-		new_ce = xcalloc(1, size);
+		new_ce = make_empty_cache_entry(istate, len);
 		memcpy(new_ce->name, ce->name, len);
 		new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
 		new_ce->ce_namelen = len;
@@ -2763,3 +2794,8 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	dst->untracked = src->untracked;
 	src->untracked = NULL;
 }
+
+void discard_cache_entry(struct cache_entry *ce)
+{
+	free(ce);
+}
diff --git a/resolve-undo.c b/resolve-undo.c
index fc5b3b83d9..966c5b5f84 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,7 +146,9 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], ru->oid[i].hash,
+		nce = make_cache_entry(istate,
+				       ru->mode[i],
+				       ru->oid[i].hash,
 				       name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
diff --git a/split-index.c b/split-index.c
index 660c75f31f..317900db8b 100644
--- a/split-index.c
+++ b/split-index.c
@@ -123,7 +123,7 @@ static void replace_entry(size_t pos, void *data)
 	src->ce_flags |= CE_UPDATE_IN_BASE;
 	src->ce_namelen = dst->ce_namelen;
 	copy_cache_entry(dst, src);
-	free(src);
+	discard_cache_entry(src);
 	si->nr_replacements++;
 }
 
@@ -224,7 +224,7 @@ void prepare_to_write_split_index(struct index_state *istate)
 			base->ce_flags = base_flags;
 			if (ret)
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
-			free(base);
+			discard_cache_entry(base);
 			si->base->cache[ce->index - 1] = ce;
 		}
 		for (i = 0; i < si->base->cache_nr; i++) {
@@ -301,7 +301,7 @@ void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce
 	    ce == istate->split_index->base->cache[ce->index - 1])
 		ce->ce_flags |= CE_REMOVE;
 	else
-		free(ce);
+		discard_cache_entry(ce);
 }
 
 void replace_index_entry_in_base(struct index_state *istate,
@@ -314,7 +314,7 @@ void replace_index_entry_in_base(struct index_state *istate,
 	    old_entry->index <= istate->split_index->base->cache_nr) {
 		new_entry->index = old_entry->index;
 		if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
-			free(istate->split_index->base->cache[new_entry->index - 1]);
+			discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
 		istate->split_index->base->cache[new_entry->index - 1] = new_entry;
 	}
 }
diff --git a/tree.c b/tree.c
index 244eb5e665..5111ce8376 100644
--- a/tree.c
+++ b/tree.c
@@ -16,15 +16,13 @@ static int read_one_entry_opt(struct index_state *istate,
 			      unsigned mode, int stage, int opt)
 {
 	int len;
-	unsigned int size;
 	struct cache_entry *ce;
 
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 
 	len = strlen(pathname);
-	size = cache_entry_size(baselen + len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, baselen + len);
 
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(stage);
diff --git a/unpack-trees.c b/unpack-trees.c
index 3a85a02a77..15f10f0055 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -203,10 +203,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce)
+static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
 {
 	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = xmalloc(size);
+	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
 
 	memcpy(new_entry, ce, size);
 	return new_entry;
@@ -216,7 +216,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce), set, clear);
+	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -797,10 +797,17 @@ static int ce_in_traverse_path(const struct cache_entry *ce,
 	return (info->pathlen < ce_namelen(ce));
 }
 
-static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
+static struct cache_entry *create_ce_entry(const struct traverse_info *info,
+					   const struct name_entry *n,
+					   int stage,
+					   struct index_state *istate,
+					   int is_transient)
 {
 	int len = traverse_path_len(info, n);
-	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
+	struct cache_entry *ce =
+		is_transient ?
+		make_empty_transient_cache_entry(len) :
+		make_empty_cache_entry(istate, len);
 
 	ce->ce_mode = create_ce_mode(n->mode);
 	ce->ce_flags = create_ce_flags(stage);
@@ -846,7 +853,15 @@ static int unpack_nondirectories(int n, unsigned long mask,
 			stage = 3;
 		else
 			stage = 2;
-		src[i + o->merge] = create_ce_entry(info, names + i, stage);
+
+		/*
+		 * If the merge bit is set, then the cache entries are
+		 * discarded in the following block.  In this case,
+		 * construct "transient" cache_entries, as they are
+		 * not stored in the index.  otherwise construct the
+		 * cache entry from the index aware logic.
+		 */
+		src[i + o->merge] = create_ce_entry(info, names + i, stage, &o->result, o->merge);
 	}
 
 	if (o->merge) {
@@ -855,7 +870,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		for (i = 0; i < n; i++) {
 			struct cache_entry *ce = src[i + o->merge];
 			if (ce != o->df_conflict_entry)
-				free(ce);
+				discard_cache_entry(ce);
 		}
 		return rc;
 	}
@@ -1787,7 +1802,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce);
+	struct cache_entry *merge = dup_entry(ce, &o->result);
 
 	if (!old) {
 		/*
@@ -1807,7 +1822,7 @@ static int merged_entry(const struct cache_entry *ce,
 
 		if (verify_absent(merge,
 				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
-			free(merge);
+			discard_cache_entry(merge);
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
@@ -1833,7 +1848,7 @@ static int merged_entry(const struct cache_entry *ce,
 			update = 0;
 		} else {
 			if (verify_uptodate(old, o)) {
-				free(merge);
+				discard_cache_entry(merge);
 				return -1;
 			}
 			/* Migrate old flags over */
-- 
2.14.3

Re: [PATCH v4 2/8] block alloc: add lifecycle APIs for cache_entry structs

[Stefan Beller]

> --- a/cache.h
> +++ b/cache.h
> @@ -339,6 +339,29 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
>  extern void free_name_hash(struct index_state *istate);
>
>
> +/* Cache entry creation and cleanup */
> +
> +/*
> + * Create cache_entry intended for use in the specified index. Caller
> + * is responsible for discarding the cache_entry with
> + * `discard_cache_entry`.
> + */
> +extern struct cache_entry *make_cache_entry(struct index_state *istate, unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);

How much work is it to convert these to object_id while at it instead
of char *sha1?
(I think we really dislike introducing new sha1 based code; If it
doesn't sound easy
maybe we can have a static inline wrapper here that just converts oid
to sha1 and
then calls this function?)

Is it possible to line break these functions (c.f. refs.h which I
think has one of
the best styles in the git project. It has long parameter lists, but
still manages
to stay below a reasonable line length) ?

> +extern struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t name_len);

> +
> +/*
> + * Create a cache_entry that is not intended to be added to an index.
> + * Caller is responsible for discarding the cache_entry
> + * with `discard_cache_entry`.
> + */
> +extern struct cache_entry *make_transient_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage);
> +extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
> +
> +/*
> + * Discard cache entry.
> + */
> +void discard_cache_entry(struct cache_entry *ce);

Please be consistent in the use of the extern keyword and omit them at all
times here and above.

RE: [PATCH v4 2/8] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

> How much work is it to convert these to object_id while at it instead of char
> *sha1?
> (I think we really dislike introducing new sha1 based code; If it doesn't sound
> easy maybe we can have a static inline wrapper here that just converts oid to
> sha1 and then calls this function?)

I have made this change in my latest patch series with 0ac48f3af7 ("read-cache: make_cache_entry should take object_id struct", 2018-06-22)

> 
> Is it possible to line break these functions (c.f. refs.h which I think has one of the
> best styles in the git project. It has long parameter lists, but still manages to stay
> below a reasonable line length) ?
> 
> > +extern struct cache_entry *make_empty_cache_entry(struct index_state
> > +*istate, size_t name_len);
> 

I have formatted the function declarations to break them up

> > +
> > +/*
> > + * Create a cache_entry that is not intended to be added to an index.
> > + * Caller is responsible for discarding the cache_entry
> > + * with `discard_cache_entry`.
> > + */
> > +extern struct cache_entry *make_transient_cache_entry(unsigned int
> > +mode, const unsigned char *sha1, const char *path, int stage); extern
> > +struct cache_entry *make_empty_transient_cache_entry(size_t
> > +name_len);
> > +
> > +/*
> > + * Discard cache entry.
> > + */
> > +void discard_cache_entry(struct cache_entry *ce);
> 
> Please be consistent in the use of the extern keyword and omit them at all times
> here and above.

The header file is a bit inconsistent overall, but I switched my declarations to not use the extern keyword.

[PATCH v4 3/8] mem-pool: only search head block for available space

[Jameson Miller]

Instead of searching all memory blocks for available space to fulfill
a memory request, only search the head block. If the head block does
not have space, assume that previous block would most likely not be
able to fulfill request either. This could potentially lead to more
memory fragmentation, but also avoids searching memory blocks that
probably will not be able to fulfill request.

This pattern will benefit consumers that are able to generate a good
estimate for how much memory will be needed, or if they are performing
fixed sized allocations, so that once a block is exhausted it will
never be able to fulfill a future request.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index 389d7af447..c80124f1fe 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -21,16 +21,16 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
-	struct mp_block *p;
+	struct mp_block *p = NULL;
 	void *r;
 
 	/* round up to a 'uintmax_t' alignment */
 	if (len & (sizeof(uintmax_t) - 1))
 		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
 
-	for (p = mem_pool->mp_block; p; p = p->next_block)
-		if (p->end - p->next_free >= len)
-			break;
+	if (mem_pool->mp_block &&
+	    mem_pool->mp_block->end - mem_pool->mp_block->next_free >= len)
+		p = mem_pool->mp_block;
 
 	if (!p) {
 		if (len >= (mem_pool->block_alloc / 2)) {
-- 
2.14.3

Re: [PATCH v4 3/8] mem-pool: only search head block for available space

[Stefan Beller]

On Wed, Jun 20, 2018 at 1:17 PM Jameson Miller <jamill@microsoft.com> wrote:
>
> Instead of searching all memory blocks for available space to fulfill
> a memory request, only search the head block. If the head block does
> not have space, assume that previous block would most likely not be
> able to fulfill request either. This could potentially lead to more
> memory fragmentation, but also avoids searching memory blocks that
> probably will not be able to fulfill request.

Do we have any numbers on performance or memory pressure here?
(I would think benchmarking fast-import would suffice as that is where
the mem pool originated)

> This pattern will benefit consumers that are able to generate a good
> estimate for how much memory will be needed, or if they are performing
> fixed sized allocations, so that once a block is exhausted it will
> never be able to fulfill a future request.

Would this be a good candidate to contain parts of
https://public-inbox.org/git/DM5PR21MB07803E8D2627676788659E63CE770@DM5PR21MB0780.namprd21.prod.outlook.com/
?

RE: [PATCH v4 3/8] mem-pool: only search head block for available space

[Jameson Miller]

> Do we have any numbers on performance or memory pressure here?
> (I would think benchmarking fast-import would suffice as that is where the mem
> pool originated)

I ran fast-import on the git.git and linux.git repositories - this action reports the 
overall memory allocated to pools. The overall memory used by pools did not change
in my tests (git.git used 2 blocks, and linux.git used 12 blocks). I included this information
in the corresponding commit message.

> 
> > This pattern will benefit consumers that are able to generate a good
> > estimate for how much memory will be needed, or if they are performing
> > fixed sized allocations, so that once a block is exhausted it will
> > never be able to fulfill a future request.
> 
> Would this be a good candidate to contain parts of

I included these details in the commit message that adds the field indicating the
cache_entry was allocated from a mem-pool.

[PATCH v4 4/8] mem-pool: tweak math on mp_block allocation size

[Jameson Miller]

The amount of memory to allocate for mp_blocks was off by a
sizeof(uintmax_t) on platforms that do not support flexible arrays. To
account for this, use the offset of the space field when calculating
the total amount of memory to allocate for a mp_block.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index c80124f1fe..a5d5eed923 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -8,9 +8,11 @@
 static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
 {
 	struct mp_block *p;
+	size_t total_alloc = st_add(offsetof(struct mp_block, space), block_alloc);
+
+	mem_pool->pool_alloc = st_add(mem_pool->pool_alloc, total_alloc);
+	p = xmalloc(total_alloc);
 
-	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
-	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
 	p->next_block = mem_pool->mp_block;
 	p->next_free = (char *)p->space;
 	p->end = p->next_free + block_alloc;
-- 
2.14.3

[PATCH v4 5/8] mem-pool: add lifecycle management functions

[Jameson Miller]

Add initialization and discard functions to mem_pool type. As the
memory allocated by mem_pool can now be freed, we also track the large
memory alllocations so they can be freed as well.

If the there are existing mp_blocks in the mem_pool's linked list of
mp_blocks, then the mp_block for a large allocation is inserted
after the head block. This is because only the head mp_block is considered
when searching for availble space. This results in the following
desirable properties:

1) The mp_block allocated for the large request will not be included
in the search for available space in future requests, as the large
mp_block is sized for the specific request and does not contain any
spare space.

2) The head mp_block will not bumped from considation for future
memory requests just because a request for a large chunk of memory
came in.

These changes are in preparation for a future commit that will utilize
creating and discarding memory pool.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++------------
 mem-pool.h | 10 ++++++++++
 2 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index a5d5eed923..4e544459e9 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -5,7 +5,14 @@
 #include "cache.h"
 #include "mem-pool.h"
 
-static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
+#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
+
+/*
+ * Allocate a new mp_block and insert it after the block specified in
+ * `insert_after`. If `insert_after` is NULL, then insert block at the
+ * head of the linked list.
+ */
+static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc, struct mp_block *insert_after)
 {
 	struct mp_block *p;
 	size_t total_alloc = st_add(offsetof(struct mp_block, space), block_alloc);
@@ -13,14 +20,51 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 	mem_pool->pool_alloc = st_add(mem_pool->pool_alloc, total_alloc);
 	p = xmalloc(total_alloc);
 
-	p->next_block = mem_pool->mp_block;
 	p->next_free = (char *)p->space;
 	p->end = p->next_free + block_alloc;
-	mem_pool->mp_block = p;
+
+	if (insert_after) {
+		p->next_block = insert_after->next_block;
+		insert_after->next_block = p;
+	} else {
+		p->next_block = mem_pool->mp_block;
+		mem_pool->mp_block = p;
+	}
 
 	return p;
 }
 
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
+{
+	struct mem_pool *pool;
+
+	if (*mem_pool)
+		return;
+
+	pool = xcalloc(1, sizeof(*pool));
+
+	pool->block_alloc = BLOCK_GROWTH_SIZE;
+
+	if (initial_size > 0)
+		mem_pool_alloc_block(pool, initial_size, NULL);
+
+	*mem_pool = pool;
+}
+
+void mem_pool_discard(struct mem_pool *mem_pool)
+{
+	struct mp_block *block, *block_to_free;
+
+	while ((block = mem_pool->mp_block))
+	{
+		block_to_free = block;
+		block = block->next_block;
+		free(block_to_free);
+	}
+
+	free(mem_pool);
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p = NULL;
@@ -33,15 +77,10 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 	if (mem_pool->mp_block &&
 	    mem_pool->mp_block->end - mem_pool->mp_block->next_free >= len)
 		p = mem_pool->mp_block;
-
-	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2)) {
-			mem_pool->pool_alloc += len;
-			return xmalloc(len);
-		}
-
-		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
-	}
+	else if (len >= (mem_pool->block_alloc / 2))
+		p = mem_pool_alloc_block(mem_pool, len, mem_pool->mp_block);
+	else
+		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc, NULL);
 
 	r = p->next_free;
 	p->next_free += len;
diff --git a/mem-pool.h b/mem-pool.h
index 829ad58ecf..f75b3365d5 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -21,6 +21,16 @@ struct mem_pool {
 	size_t pool_alloc;
 };
 
+/*
+ * Initialize mem_pool with specified initial size.
+ */
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
+
+/*
+ * Discard a memory pool and free all the memory it is responsible for.
+ */
+void mem_pool_discard(struct mem_pool *mem_pool);
+
 /*
  * Alloc memory from the mem_pool.
  */
-- 
2.14.3

[PATCH v4 6/8] mem-pool: fill out functionality

[Jameson Miller]

Add functions for:

    - combining two memory pools

    - determining if a memory address is within the range managed by a
      memory pool

These functions will be used by future commits.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 mem-pool.h | 13 +++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/mem-pool.c b/mem-pool.c
index 4e544459e9..81fda969d3 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -94,3 +94,45 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	memset(r, 0, len);
 	return r;
 }
+
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
+{
+	struct mp_block *p;
+
+	/* Check if memory is allocated in a block */
+	for (p = mem_pool->mp_block; p; p = p->next_block)
+		if ((mem >= ((void *)p->space)) &&
+		    (mem < ((void *)p->end)))
+			return 1;
+
+	return 0;
+}
+
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
+{
+	struct mp_block *p;
+
+	/* Append the blocks from src to dst */
+	if (dst->mp_block && src->mp_block) {
+		/*
+		 * src and dst have blocks, append
+		 * blocks from src to dst.
+		 */
+		p = dst->mp_block;
+		while (p->next_block)
+			p = p->next_block;
+
+		p->next_block = src->mp_block;
+	} else if (src->mp_block) {
+		/*
+		 * src has blocks, dst is empty.
+		 */
+		dst->mp_block = src->mp_block;
+	} else {
+		/* src is empty, nothing to do. */
+	}
+
+	dst->pool_alloc += src->pool_alloc;
+	src->pool_alloc = 0;
+	src->mp_block = NULL;
+}
diff --git a/mem-pool.h b/mem-pool.h
index f75b3365d5..adeefdcb28 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -41,4 +41,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
+ * pool will be empty and not contain any memory. It still needs to be free'd
+ * with a call to `mem_pool_discard`.
+ */
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
+
+/*
+ * Check if a memory pointed at by 'mem' is part of the range of
+ * memory managed by the specified mem_pool.
+ */
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
+
 #endif
-- 
2.14.3

[PATCH v4 7/8] block alloc: allocate cache entries from mem_pool

[Jameson Miller]

When reading large indexes from disk, a portion of the time is
dominated in malloc() calls. This can be mitigated by allocating a
large block of memory and manage it ourselves via memory pools.

This change moves the cache entry allocation to be on top of memory
pools.

Design:

The index_state struct will gain a notion of an associated memory_pool
from which cache_entries will be allocated from. When reading in the
index from disk, we have information on the number of entries and
their size, which can guide us in deciding how large our initial
memory allocation should be. When an index is discarded, the
associated memory_pool will be discarded as well - so the lifetime of
a cache_entry is tied to the lifetime of the index_state that it was
allocated for.

In the case of a Split Index, the following rules are followed. 1st,
some terminology is defined:

Terminology:
  - 'the_index': represents the logical view of the index

  - 'split_index': represents the "base" cache entries. Read from the
    split index file.

'the_index' can reference a single split_index, as well as
cache_entries from the split_index. `the_index` will be discarded
before the `split_index` is.  This means that when we are allocating
cache_entries in the presence of a split index, we need to allocate
the entries from the `split_index`'s memory pool.  This allows us to
follow the pattern that `the_index` can reference cache_entries from
the `split_index`, and that the cache_entries will not be freed while
they are still being referenced.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h        |  21 ++++++++++
 mem-pool.c     |   3 +-
 read-cache.c   | 119 ++++++++++++++++++++++++++++++++++++++++++++++++---------
 split-index.c  |  50 ++++++++++++++++++++----
 unpack-trees.c |  13 +------
 5 files changed, 167 insertions(+), 39 deletions(-)

diff --git a/cache.h b/cache.h
index abcc27ff87..74d3ebebc2 100644
--- a/cache.h
+++ b/cache.h
@@ -15,6 +15,7 @@
 #include "path.h"
 #include "sha1-array.h"
 #include "repository.h"
+#include "mem-pool.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -156,6 +157,7 @@ struct cache_entry {
 	struct stat_data ce_stat_data;
 	unsigned int ce_mode;
 	unsigned int ce_flags;
+	unsigned int mem_pool_allocated;
 	unsigned int ce_namelen;
 	unsigned int index;	/* for link extension */
 	struct object_id oid;
@@ -227,6 +229,7 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 				    const struct cache_entry *src)
 {
 	unsigned int state = dst->ce_flags & CE_HASHED;
+	int mem_pool_allocated = dst->mem_pool_allocated;
 
 	/* Don't copy hash chain and name */
 	memcpy(&dst->ce_stat_data, &src->ce_stat_data,
@@ -235,6 +238,9 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 
 	/* Restore the hash state */
 	dst->ce_flags = (dst->ce_flags & ~CE_HASHED) | state;
+
+	/* Restore the mem_pool_allocated flag */
+	dst->mem_pool_allocated = mem_pool_allocated;
 }
 
 static inline unsigned create_ce_flags(unsigned stage)
@@ -328,6 +334,7 @@ struct index_state {
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
+	struct mem_pool *ce_mem_pool;
 };
 
 extern struct index_state the_index;
@@ -362,6 +369,20 @@ extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Duplicate a cache_entry. Allocate memory for the new entry from a
+ * memory_pool. Takes into account cache_entry fields that are meant
+ * for managing the underlying memory allocation of the cache_entry.
+ */
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce, struct index_state *istate);
+
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/mem-pool.c b/mem-pool.c
index 81fda969d3..0f19cc01a9 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -55,7 +55,8 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 {
 	struct mp_block *block, *block_to_free;
 
-	while ((block = mem_pool->mp_block))
+	block = mem_pool->mp_block;
+	while (block)
 	{
 		block_to_free = block;
 		block = block->next_block;
diff --git a/read-cache.c b/read-cache.c
index 6396e04e45..a8932ce2a6 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -46,6 +46,48 @@
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
 		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
+
+/*
+ * This is an estimate of the pathname length in the index.  We use
+ * this for V4 index files to guess the un-deltafied size of the index
+ * in memory because of pathname deltafication.  This is not required
+ * for V2/V3 index formats because their pathnames are not compressed.
+ * If the initial amount of memory set aside is not sufficient, the
+ * mem pool will allocate extra memory.
+ */
+#define CACHE_ENTRY_PATH_LENGTH 80
+
+static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry *ce;
+	ce = mem_pool_alloc(mem_pool, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry * ce;
+	ce = mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static struct mem_pool *find_mem_pool(struct index_state *istate)
+{
+	struct mem_pool **pool_ptr;
+
+	if (istate->split_index && istate->split_index->base)
+		pool_ptr = &istate->split_index->base->ce_mem_pool;
+	else
+		pool_ptr = &istate->ce_mem_pool;
+
+	if (!*pool_ptr)
+		mem_pool_init(pool_ptr, 0);
+
+	return *pool_ptr;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -746,7 +788,7 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 
 struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
 {
-	return xcalloc(1, cache_entry_size(len));
+	return mem_pool__ce_calloc(find_mem_pool(istate), len);
 }
 
 struct cache_entry *make_empty_transient_cache_entry(size_t len)
@@ -1665,13 +1707,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+static struct cache_entry *cache_entry_from_ondisk(struct mem_pool *mem_pool,
 						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = make_empty_cache_entry(istate, len);
+	struct cache_entry *ce = mem_pool__ce_alloc(mem_pool, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1713,7 +1755,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct index_state *istate,
+static struct cache_entry *create_from_disk(struct mem_pool *mem_pool,
 					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
@@ -1745,13 +1787,13 @@ static struct cache_entry *create_from_disk(struct index_state *istate,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags,
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1825,6 +1867,22 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_fsmonitor(istate);
 }
 
+static size_t estimate_cache_size_from_compressed(unsigned int entries)
+{
+	return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_PATH_LENGTH);
+}
+
+static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
+{
+	long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
+
+	/*
+	 * Account for potential alignment differences.
+	 */
+	per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	return ondisk_size + entries * per_entry;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1871,10 +1929,15 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
 	istate->initialized = 1;
 
-	if (istate->version == 4)
+	if (istate->version == 4) {
 		previous_name = &previous_name_buf;
-	else
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size_from_compressed(istate->cache_nr));
+	} else {
 		previous_name = NULL;
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size(mmap_size, istate->cache_nr));
+	}
 
 	src_offset = sizeof(*hdr);
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -1883,7 +1946,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate->ce_mem_pool, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1980,17 +2043,13 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-	int i;
+	/*
+	 * Cache entries in istate->cache[] should have been allocated
+	 * from the memory pool associated with this index, or from an
+	 * associated split_index. There is no need to free individual
+	 * cache entries.
+	 */
 
-	for (i = 0; i < istate->cache_nr; i++) {
-		if (istate->cache[i]->index &&
-		    istate->split_index &&
-		    istate->split_index->base &&
-		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-			continue;
-		discard_cache_entry(istate->cache[i]);
-	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -2004,6 +2063,12 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool);
+		istate->ce_mem_pool = NULL;
+	}
+
 	return 0;
 }
 
@@ -2795,7 +2860,23 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	src->untracked = NULL;
 }
 
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
+				    struct index_state *istate)
+{
+	unsigned int size = ce_size(ce);
+	int mem_pool_allocated;
+	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
+	mem_pool_allocated = new_entry->mem_pool_allocated;
+
+	memcpy(new_entry, ce, size);
+	new_entry->mem_pool_allocated = mem_pool_allocated;
+	return new_entry;
+}
+
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && ce->mem_pool_allocated)
+		return;
+
 	free(ce);
 }
diff --git a/split-index.c b/split-index.c
index 317900db8b..84f067e10d 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,16 +73,31 @@ void move_cache_to_base_index(struct index_state *istate)
 	int i;
 
 	/*
-	 * do not delete old si->base, its index entries may be shared
-	 * with istate->cache[]. Accept a bit of leaking here because
-	 * this code is only used by short-lived update-index.
+	 * If there was a previous base index, then transfer ownership of allocated
+	 * entries to the parent index.
 	 */
+	if (si->base &&
+		si->base->ce_mem_pool) {
+
+		if (!istate->ce_mem_pool)
+			mem_pool_init(&istate->ce_mem_pool, 0);
+
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+	}
+
 	si->base = xcalloc(1, sizeof(*si->base));
 	si->base->version = istate->version;
 	/* zero timestamp disables racy test in ce_write_index() */
 	si->base->timestamp = istate->timestamp;
 	ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
 	si->base->cache_nr = istate->cache_nr;
+
+	/*
+	 * The mem_pool needs to move with the allocated entries.
+	 */
+	si->base->ce_mem_pool = istate->ce_mem_pool;
+	istate->ce_mem_pool = NULL;
+
 	COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
 	mark_base_index_entries(si->base);
 	for (i = 0; i < si->base->cache_nr; i++)
@@ -331,12 +346,31 @@ void remove_split_index(struct index_state *istate)
 {
 	if (istate->split_index) {
 		/*
-		 * can't discard_split_index(&the_index); because that
-		 * will destroy split_index->base->cache[], which may
-		 * be shared with the_index.cache[]. So yeah we're
-		 * leaking a bit here.
+		 * When removing the split index, we need to move
+		 * ownership of the mem_pool associated with the
+		 * base index to the main index. There may be cache entries
+		 * allocated from the base's memory pool that are shared with
+		 * the_index.cache[].
 		 */
-		istate->split_index = NULL;
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+
+		/*
+		 * The split index no longer owns the mem_pool backing
+		 * its cache array. As we are discarding this index,
+		 * mark the index as having no cache entries, so it
+		 * will not attempt to clean up the cache entries or
+		 * validate them.
+		 */
+		if (istate->split_index->base)
+			istate->split_index->base->cache_nr = 0;
+
+		/*
+		 * We can discard the split index because its
+		 * memory pool has been incorporated into the
+		 * memory pool associated with the the_index.
+		 */
+		discard_split_index(istate);
+
 		istate->cache_changed |= SOMETHING_CHANGED;
 	}
 }
diff --git a/unpack-trees.c b/unpack-trees.c
index 15f10f0055..907126dff4 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -203,20 +203,11 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
-{
-	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
-
-	memcpy(new_entry, ce, size);
-	return new_entry;
-}
-
 static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
+	do_add_entry(o, dup_cache_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -1802,7 +1793,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce, &o->result);
+	struct cache_entry *merge = dup_cache_entry(ce, &o->result);
 
 	if (!old) {
 		/*
-- 
2.14.3

[PATCH v4 8/8] block alloc: add validations around cache_entry lifecyle

[Jameson Miller]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h      |  6 ++++++
 git.c        |  3 +++
 mem-pool.c   |  6 +++++-
 mem-pool.h   |  2 +-
 read-cache.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 5 files changed, 68 insertions(+), 4 deletions(-)

diff --git a/cache.h b/cache.h
index 74d3ebebc2..c0d6b976f5 100644
--- a/cache.h
+++ b/cache.h
@@ -369,6 +369,12 @@ extern struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Check configuration if we should perform extra validation on cache
+ * entries.
+ */
+int should_validate_cache_entries(void);
+
 /*
  * Duplicate a cache_entry. Allocate memory for the new entry from a
  * memory_pool. Takes into account cache_entry fields that are meant
diff --git a/git.c b/git.c
index c2f48d53dd..010898ba6d 100644
--- a/git.c
+++ b/git.c
@@ -414,7 +414,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index 0f19cc01a9..92d106a637 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -51,7 +51,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
 	*mem_pool = pool;
 }
 
-void mem_pool_discard(struct mem_pool *mem_pool)
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory)
 {
 	struct mp_block *block, *block_to_free;
 
@@ -60,6 +60,10 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 	{
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
diff --git a/mem-pool.h b/mem-pool.h
index adeefdcb28..999d3c3a52 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -29,7 +29,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
 /*
  * Discard a memory pool and free all the memory it is responsible for.
  */
-void mem_pool_discard(struct mem_pool *mem_pool);
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory);
 
 /*
  * Alloc memory from the mem_pool.
diff --git a/read-cache.c b/read-cache.c
index a8932ce2a6..2652f2aeb0 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2047,8 +2047,10 @@ int discard_index(struct index_state *istate)
 	 * Cache entries in istate->cache[] should have been allocated
 	 * from the memory pool associated with this index, or from an
 	 * associated split_index. There is no need to free individual
-	 * cache entries.
+	 * cache entries. validate_cache_entries can detect when this
+	 * assertion does not hold.
 	 */
+	validate_cache_entries(istate);
 
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2065,13 +2067,45 @@ int discard_index(struct index_state *istate)
 	istate->untracked = NULL;
 
 	if (istate->ce_mem_pool) {
-		mem_pool_discard(istate->ce_mem_pool);
+		mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
 		istate->ce_mem_pool = NULL;
 	}
 
 	return 0;
 }
 
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+
+	if (!should_validate_cache_entries() ||!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2875,8 +2909,25 @@ struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
 
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && should_validate_cache_entries())
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
+
 	if (ce && ce->mem_pool_allocated)
 		return;
 
 	free(ce);
 }
+
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
-- 
2.14.3

[PATCH v5 0/8] Allocate cache entries from mem_pool

[Jameson Miller]

Changes from v4 are minor code review feedback items:

  - Remove extern keyword from new function definitions in cache.h
  - Make_cache_entry(..) functions work with object_id instead of sha
  - Add details to commit message for "block alloc: allocate cache entries from mem_pool"
  - Add details to commit message for "mem-pool: only search head block for available space"

The largest change is the new commit "read-cache: make_cache_entry should take object_id struct"

Base Ref: master
Web-Diff: https://github.com/jamill/git/compare/ed843436dd...55c9b9008f

Jameson Miller (8):
  read-cache: teach refresh_cache_entry() to take istate
  read-cache: make_cache_entry should take object_id struct
  block alloc: add lifecycle APIs for cache_entry structs
  mem-pool: only search head block for available space
  mem-pool: add life cycle management functions
  mem-pool: fill out functionality
  block alloc: allocate cache entries from mem-pool
  block alloc: add validations around cache_entry lifecyle

 apply.c                |  24 ++--
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   6 +-
 builtin/reset.c        |   2 +-
 builtin/update-index.c |  26 ++--
 cache.h                |  64 +++++++++-
 git.c                  |   3 +
 mem-pool.c             | 114 ++++++++++++++++--
 mem-pool.h             |  23 ++++
 merge-recursive.c      |   4 +-
 read-cache.c           | 264 ++++++++++++++++++++++++++++++++++-------
 resolve-undo.c         |   4 +-
 split-index.c          |  58 +++++++--
 tree.c                 |   4 +-
 unpack-trees.c         |  40 ++++---
 16 files changed, 515 insertions(+), 134 deletions(-)


base-commit: ed843436dd4924c10669820cc73daf50f0b4dabd
-- 
2.17.1

[PATCH v5 1/8] read-cache: teach refresh_cache_entry() to take istate

[Jameson Miller]

Refactor refresh_cache_entry() to work on a specific index, instead of
implicitly using the_index. This is in preparation for making the
make_cache_entry function apply to a specific index.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h           | 2 +-
 merge-recursive.c | 2 +-
 read-cache.c      | 9 +++++----
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/cache.h b/cache.h
index d49092d94d..93af25f586 100644
--- a/cache.h
+++ b/cache.h
@@ -751,7 +751,7 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 #define REFRESH_IGNORE_SUBMODULES	0x0010	/* ignore submodules */
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
-extern struct cache_entry *refresh_cache_entry(struct cache_entry *, unsigned int);
+extern struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 /*
  * Opportunistically update the index but do not complain if we can't.
diff --git a/merge-recursive.c b/merge-recursive.c
index bed4a5be02..8b3d6781c7 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -326,7 +326,7 @@ static int add_cacheinfo(struct merge_options *o,
 	if (refresh) {
 		struct cache_entry *nce;
 
-		nce = refresh_cache_entry(ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		nce = refresh_cache_entry(&the_index, ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
 		if (!nce)
 			return err(o, _("add_cacheinfo failed to refresh for path '%s'; merge aborting."), path);
 		if (nce != ce)
diff --git a/read-cache.c b/read-cache.c
index 372588260e..fa8366ecab 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -767,7 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	ce->ce_namelen = len;
 	ce->ce_mode = create_ce_mode(mode);
 
-	ret = refresh_cache_entry(ce, refresh_options);
+	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
 		free(ce);
 	return ret;
@@ -1473,10 +1473,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	return has_errors;
 }
 
-struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
-					       unsigned int options)
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+					struct cache_entry *ce,
+					unsigned int options)
 {
-	return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
-- 
2.17.1

[PATCH v5 2/8] read-cache: make_cache_entry should take object_id struct

[Jameson Miller]

The make_cache_entry function should take an object_id struct instead
of sha.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 apply.c            | 2 +-
 builtin/checkout.c | 2 +-
 builtin/difftool.c | 4 ++--
 builtin/reset.c    | 2 +-
 cache.h            | 7 ++++++-
 merge-recursive.c  | 2 +-
 read-cache.c       | 8 +++++---
 resolve-undo.c     | 2 +-
 8 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/apply.c b/apply.c
index 959c457910..8ef975a32d 100644
--- a/apply.c
+++ b/apply.c
@@ -4092,7 +4092,7 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
+		ce = make_cache_entry(patch->old_mode, &oid, name, 0, 0);
 		if (!ce)
 			return error(_("make_cache_entry failed for path '%s'"),
 				     name);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 2e1d2376d2..548bf40f25 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -230,7 +230,7 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_cache_entry(mode, &oid, path, 2, 0);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
diff --git a/builtin/difftool.c b/builtin/difftool.c
index bc97d4aef2..873a06f0d9 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,7 +321,7 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ce = make_cache_entry(mode, oid, path, 0, 0);
 	ret = checkout_entry(ce, state, NULL);
 
 	free(ce);
@@ -488,7 +488,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
+					make_cache_entry(rmode, &roid,
 							 dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
diff --git a/builtin/reset.c b/builtin/reset.c
index a862c70fab..00109b041f 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,7 +134,7 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, one->oid.hash, one->path,
+		ce = make_cache_entry(one->mode, &one->oid, one->path,
 				      0, 0);
 		if (!ce)
 			die(_("make_cache_entry failed for path '%s'"),
diff --git a/cache.h b/cache.h
index 93af25f586..3fbf24771a 100644
--- a/cache.h
+++ b/cache.h
@@ -698,7 +698,12 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
+extern struct cache_entry *make_cache_entry(unsigned int mode,
+					    const struct object_id *oid,
+					    const char *path,
+					    int stage,
+					    unsigned int refresh_options);
+
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 8b3d6781c7..873321e5c2 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -318,7 +318,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid->hash : null_sha1, path, stage, 0);
+	ce = make_cache_entry(mode, oid ? oid : &null_oid, path, stage, 0);
 	if (!ce)
 		return err(o, _("add_cacheinfo failed for path '%s'; merge aborting."), path);
 
diff --git a/read-cache.c b/read-cache.c
index fa8366ecab..9624ce1784 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -746,8 +746,10 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 }
 
 struct cache_entry *make_cache_entry(unsigned int mode,
-		const unsigned char *sha1, const char *path, int stage,
-		unsigned int refresh_options)
+				     const struct object_id *oid,
+				     const char *path,
+				     int stage,
+				     unsigned int refresh_options)
 {
 	int size, len;
 	struct cache_entry *ce, *ret;
@@ -761,7 +763,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	size = cache_entry_size(len);
 	ce = xcalloc(1, size);
 
-	hashcpy(ce->oid.hash, sha1);
+	hashcpy(ce->oid.hash, oid->hash);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(stage);
 	ce->ce_namelen = len;
diff --git a/resolve-undo.c b/resolve-undo.c
index fc5b3b83d9..4d4e5cb6bf 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,7 +146,7 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], ru->oid[i].hash,
+		nce = make_cache_entry(ru->mode[i], &ru->oid[i],
 				       name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
-- 
2.17.1

Re: [PATCH v5 2/8] read-cache: make_cache_entry should take object_id struct

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> The make_cache_entry function should take an object_id struct instead
> of sha.

The name of the hash is SHA-1, not sha ;-)

It is not worth a reroll, but I do not think "should" is a
particularly good thing to say in the title or justification in the
log message in this case.  It is more like you (or somebody else who
commented) _want_ to make it take an oid for _some_ reason.  "teach
make_cache_entry() to take object_id" is probably a better title
that admits that we do not explicitly say _why_ we are doing so,
than saying "it should", which equally is not explicit ;-)

> diff --git a/read-cache.c b/read-cache.c
> index fa8366ecab..9624ce1784 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -746,8 +746,10 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
>  }
>  
>  struct cache_entry *make_cache_entry(unsigned int mode,
> -		const unsigned char *sha1, const char *path, int stage,
> -		unsigned int refresh_options)
> +				     const struct object_id *oid,
> +				     const char *path,
> +				     int stage,
> +				     unsigned int refresh_options)
>  {
>  	int size, len;
>  	struct cache_entry *ce, *ret;
> @@ -761,7 +763,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
>  	size = cache_entry_size(len);
>  	ce = xcalloc(1, size);
>  
> -	hashcpy(ce->oid.hash, sha1);
> +	hashcpy(ce->oid.hash, oid->hash);
>  	memcpy(ce->name, path, len);
>  	ce->ce_flags = create_ce_flags(stage);
>  	ce->ce_namelen = len;

The patch itself looks good.

Thanks.

Re: [PATCH v5 2/8] read-cache: make_cache_entry should take object_id struct

[SZEDER Gábor]

> The make_cache_entry function should take an object_id struct instead
> of sha.


> diff --git a/read-cache.c b/read-cache.c
> index fa8366ecab..9624ce1784 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -746,8 +746,10 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
>  }
> 
>  struct cache_entry *make_cache_entry(unsigned int mode,
> -		const unsigned char *sha1, const char *path, int stage,
> -		unsigned int refresh_options)
> +				     const struct object_id *oid,
> +				     const char *path,
> +				     int stage,
> +				     unsigned int refresh_options)
>  {
>  	int size, len;
>  	struct cache_entry *ce, *ret;
> @@ -761,7 +763,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
>  	size = cache_entry_size(len);
>  	ce = xcalloc(1, size);
> 
> -	hashcpy(ce->oid.hash, sha1);
> +	hashcpy(ce->oid.hash, oid->hash);

Speaking of using struct object_id instead of sha, please use oidcpy()
here.

[PATCH v5 3/8] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

Add an API around managing the lifetime of cache_entry
structs. Abstracting memory management details behind this API will
allow for alternative memory management strategies without affecting
all the call sites.  This commit does not change how memory is
allocated or freed. A later commit in this series will allocate cache
entries from memory pools as appropriate.

Motivation:
It has been observed that the time spent loading an index with a large
number of entries is partly dominated by malloc() calls. This change
is in preparation for using memory pools to reduce the number of
malloc() calls made when loading an index.

This API makes a distinction between cache entries that are intended
for use with a particular index and cache entries that are not. This
enables us to use the knowledge about how a cache entry will be used
to make informed decisions about how to handle the corresponding
memory.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 apply.c                | 24 +++++------
 blame.c                |  5 +--
 builtin/checkout.c     |  8 ++--
 builtin/difftool.c     |  6 +--
 builtin/reset.c        |  2 +-
 builtin/update-index.c | 26 +++++-------
 cache.h                | 40 +++++++++++++++---
 merge-recursive.c      |  2 +-
 read-cache.c           | 93 +++++++++++++++++++++++++++++-------------
 resolve-undo.c         |  4 +-
 split-index.c          |  8 ++--
 tree.c                 |  4 +-
 unpack-trees.c         | 35 +++++++++++-----
 13 files changed, 165 insertions(+), 92 deletions(-)

diff --git a/apply.c b/apply.c
index 8ef975a32d..8a4a4439bc 100644
--- a/apply.c
+++ b/apply.c
@@ -4092,12 +4092,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, &oid, name, 0, 0);
+		ce = make_cache_entry(&result, patch->old_mode, &oid, name, 0, 0);
 		if (!ce)
 			return error(_("make_cache_entry failed for path '%s'"),
 				     name);
 		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("could not add %s to temporary index"),
 				     name);
 		}
@@ -4265,9 +4265,8 @@ static int add_index_file(struct apply_state *state,
 	struct stat st;
 	struct cache_entry *ce;
 	int namelen = strlen(path);
-	unsigned ce_size = cache_entry_size(namelen);
 
-	ce = xcalloc(1, ce_size);
+	ce = make_empty_cache_entry(&the_index, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(0);
@@ -4280,13 +4279,13 @@ static int add_index_file(struct apply_state *state,
 
 		if (!skip_prefix(buf, "Subproject commit ", &s) ||
 		    get_oid_hex(s, &ce->oid)) {
-			free(ce);
-		       return error(_("corrupt patch for submodule %s"), path);
+			discard_cache_entry(ce);
+			return error(_("corrupt patch for submodule %s"), path);
 		}
 	} else {
 		if (!state->cached) {
 			if (lstat(path, &st) < 0) {
-				free(ce);
+				discard_cache_entry(ce);
 				return error_errno(_("unable to stat newly "
 						     "created file '%s'"),
 						   path);
@@ -4294,13 +4293,13 @@ static int add_index_file(struct apply_state *state,
 			fill_stat_cache_info(ce, &st);
 		}
 		if (write_object_file(buf, size, blob_type, &ce->oid) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to create backing store "
 				       "for newly created file %s"), path);
 		}
 	}
 	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error(_("unable to add cache entry for %s"), path);
 	}
 
@@ -4424,27 +4423,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
 				       struct patch *patch)
 {
 	int stage, namelen;
-	unsigned ce_size, mode;
+	unsigned mode;
 	struct cache_entry *ce;
 
 	if (!state->update_index)
 		return 0;
 	namelen = strlen(patch->new_name);
-	ce_size = cache_entry_size(namelen);
 	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
 
 	remove_file_from_cache(patch->new_name);
 	for (stage = 1; stage < 4; stage++) {
 		if (is_null_oid(&patch->threeway_stage[stage - 1]))
 			continue;
-		ce = xcalloc(1, ce_size);
+		ce = make_empty_cache_entry(&the_index, namelen);
 		memcpy(ce->name, patch->new_name, namelen);
 		ce->ce_mode = create_ce_mode(mode);
 		ce->ce_flags = create_ce_flags(stage);
 		ce->ce_namelen = namelen;
 		oidcpy(&ce->oid, &patch->threeway_stage[stage - 1]);
 		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to add cache entry for %s"),
 				     patch->new_name);
 		}
diff --git a/blame.c b/blame.c
index a5c9bd78ab..87dade745c 100644
--- a/blame.c
+++ b/blame.c
@@ -173,7 +173,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
 	time_t now;
-	int size, len;
+	int len;
 	struct cache_entry *ce;
 	unsigned mode;
 	struct strbuf msg = STRBUF_INIT;
@@ -271,8 +271,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 			/* Let's not bother reading from HEAD tree */
 			mode = S_IFREG | 0644;
 	}
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, &origin->blob_oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 548bf40f25..56d1e1a28d 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -77,7 +77,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -96,7 +96,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		if (ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
@@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, &oid, path, 2, 0);
+	ce = make_transient_cache_entry(mode, &oid, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	discard_cache_entry(ce);
 	return status;
 }
 
diff --git a/builtin/difftool.c b/builtin/difftool.c
index 873a06f0d9..4593f0c2cd 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,10 +321,10 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid, path, 0, 0);
+	ce = make_transient_cache_entry(mode, oid, path, 0);
 	ret = checkout_entry(ce, state, NULL);
 
-	free(ce);
+	discard_cache_entry(ce);
 	return ret;
 }
 
@@ -488,7 +488,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, &roid,
+					make_cache_entry(&wtindex, rmode, &roid,
 							 dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
diff --git a/builtin/reset.c b/builtin/reset.c
index 00109b041f..c3f0cfa1e8 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,7 +134,7 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, &one->oid, one->path,
+		ce = make_cache_entry(&the_index, one->mode, &one->oid, one->path,
 				      0, 0);
 		if (!ce)
 			die(_("make_cache_entry failed for path '%s'"),
diff --git a/builtin/update-index.c b/builtin/update-index.c
index a8709a26ec..ea2f2a476c 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -268,15 +268,14 @@ static int process_lstat_error(const char *path, int err)
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
-	int option, size;
+	int option;
 	struct cache_entry *ce;
 
 	/* Was the old index entry already up-to-date? */
 	if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
 		return 0;
 
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
@@ -285,13 +284,13 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 
 	if (index_path(&ce->oid, path, st,
 		       info_only ? 0 : HASH_WRITE_OBJECT)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return -1;
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
 	if (add_cache_entry(ce, option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
 	}
 	return 0;
@@ -402,15 +401,14 @@ static int process_path(const char *path, struct stat *st, int stat_errno)
 static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 			 const char *path, int stage)
 {
-	int size, len, option;
+	int len, option;
 	struct cache_entry *ce;
 
 	if (!verify_path(path, mode))
 		return error("Invalid path '%s'", path);
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -599,7 +597,6 @@ static struct cache_entry *read_one_ent(const char *which,
 {
 	unsigned mode;
 	struct object_id oid;
-	int size;
 	struct cache_entry *ce;
 
 	if (get_tree_entry(ent, path, &oid, &mode)) {
@@ -612,8 +609,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, namelen);
 
 	oidcpy(&ce->oid, &oid);
 	memcpy(ce->name, path, namelen);
@@ -690,8 +686,8 @@ static int unresolve_one(const char *path)
 	error("%s: cannot add their version to the index.", path);
 	ret = -1;
  free_return:
-	free(ce_2);
-	free(ce_3);
+	discard_cache_entry(ce_2);
+	discard_cache_entry(ce_3);
 	return ret;
 }
 
@@ -758,7 +754,7 @@ static int do_reupdate(int ac, const char **av,
 					   ce->name, ce_namelen(ce), 0);
 		if (old && ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
-			free(old);
+			discard_cache_entry(old);
 			continue; /* unchanged */
 		}
 		/* Be careful.  The working tree may not have the
@@ -769,7 +765,7 @@ static int do_reupdate(int ac, const char **av,
 		path = xstrdup(ce->name);
 		update_one(path);
 		free(path);
-		free(old);
+		discard_cache_entry(old);
 		if (save_nr != active_nr)
 			goto redo;
 	}
diff --git a/cache.h b/cache.h
index 3fbf24771a..035a627bea 100644
--- a/cache.h
+++ b/cache.h
@@ -339,6 +339,40 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 extern void free_name_hash(struct index_state *istate);
 
 
+/* Cache entry creation and cleanup */
+
+/*
+ * Create cache_entry intended for use in the specified index. Caller
+ * is responsible for discarding the cache_entry with
+ * `discard_cache_entry`.
+ */
+struct cache_entry *make_cache_entry(struct index_state *istate,
+				     unsigned int mode,
+				     const struct object_id *oid,
+				     const char *path,
+				     int stage,
+				     unsigned int refresh_options);
+
+struct cache_entry *make_empty_cache_entry(struct index_state *istate,
+					   size_t name_len);
+
+/*
+ * Create a cache_entry that is not intended to be added to an index.
+ * Caller is responsible for discarding the cache_entry
+ * with `discard_cache_entry`.
+ */
+struct cache_entry *make_transient_cache_entry(unsigned int mode,
+					       const struct object_id *oid,
+					       const char *path,
+					       int stage);
+
+struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
+
+/*
+ * Discard cache entry.
+ */
+void discard_cache_entry(struct cache_entry *ce);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
@@ -698,12 +732,6 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode,
-					    const struct object_id *oid,
-					    const char *path,
-					    int stage,
-					    unsigned int refresh_options);
-
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 873321e5c2..06d77afbeb 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -318,7 +318,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid : &null_oid, path, stage, 0);
+	ce = make_cache_entry(&the_index, mode, oid ? oid : &null_oid, path, stage, 0);
 	if (!ce)
 		return err(o, _("add_cacheinfo failed for path '%s'; merge aborting."), path);
 
diff --git a/read-cache.c b/read-cache.c
index 9624ce1784..116fd51680 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -61,7 +61,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 	replace_index_entry_in_base(istate, old, ce);
 	remove_name_hash(istate, old);
-	free(old);
+	discard_cache_entry(old);
 	ce->ce_flags &= ~CE_HASHED;
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +74,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new_entry = xmalloc(cache_entry_size(namelen));
+	new_entry = make_empty_cache_entry(istate, namelen);
 	copy_cache_entry(new_entry, old_entry);
 	new_entry->ce_flags &= ~CE_HASHED;
 	new_entry->ce_namelen = namelen;
@@ -623,7 +623,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new_entry = xcalloc(1, cache_entry_size(len));
+	new_entry = make_empty_cache_entry(istate, len);
 	memcpy(new_entry->name, alias->name, len);
 	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
@@ -640,7 +640,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-	int size, namelen, was_same;
+	int namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
@@ -662,8 +662,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_namelen = namelen;
 	if (!intent_only)
@@ -704,13 +703,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 				ce_mark_uptodate(alias);
 			alias->ce_flags |= CE_ADDED;
 
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
 	if (!intent_only) {
 		if (index_path(&ce->oid, path, st, newflags)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error("unable to index file %s", path);
 		}
 	} else
@@ -727,9 +726,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		    ce->ce_mode == alias->ce_mode);
 
 	if (pretend)
-		free(ce);
+		discard_cache_entry(ce);
 	else if (add_index_entry(istate, ce, add_option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("unable to add %s to index", path);
 	}
 	if (verbose && !was_same)
@@ -745,14 +744,25 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 	return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
+struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_empty_transient_cache_entry(size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_cache_entry(struct index_state *istate,
+				     unsigned int mode,
 				     const struct object_id *oid,
 				     const char *path,
 				     int stage,
 				     unsigned int refresh_options)
 {
-	int size, len;
 	struct cache_entry *ce, *ret;
+	int len;
 
 	if (!verify_path(path, mode)) {
 		error("Invalid path '%s'", path);
@@ -760,8 +770,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	}
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, len);
 
 	hashcpy(ce->oid.hash, oid->hash);
 	memcpy(ce->name, path, len);
@@ -771,10 +780,33 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 
 	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
-		free(ce);
+		discard_cache_entry(ce);
 	return ret;
 }
 
+struct cache_entry *make_transient_cache_entry(unsigned int mode, const struct object_id *oid,
+					       const char *path, int stage)
+{
+	struct cache_entry *ce;
+	int len;
+
+	if (!verify_path(path, mode)) {
+		error("Invalid path '%s'", path);
+		return NULL;
+	}
+
+	len = strlen(path);
+	ce = make_empty_transient_cache_entry(len);
+
+	hashcpy(ce->oid.hash, oid->hash);
+	memcpy(ce->name, path, len);
+	ce->ce_flags = create_ce_flags(stage);
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	return ce;
+}
+
 /*
  * Chmod an index entry with either +x or -x.
  *
@@ -1270,7 +1302,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
 	struct stat st;
 	struct cache_entry *updated;
-	int changed, size;
+	int changed;
 	int refresh = options & CE_MATCH_REFRESH;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
@@ -1350,8 +1382,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
-	size = ce_size(ce);
-	updated = xmalloc(size);
+	updated = make_empty_cache_entry(istate, ce_namelen(ce));
 	copy_cache_entry(updated, ce);
 	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
 	fill_stat_cache_info(updated, &st);
@@ -1637,12 +1668,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = xmalloc(cache_entry_size(len));
+	struct cache_entry *ce = make_empty_cache_entry(istate, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1684,7 +1716,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *create_from_disk(struct index_state *istate,
+					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
 {
@@ -1715,13 +1748,13 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(ondisk, flags,
+		ce = cache_entry_from_ondisk(istate, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1853,7 +1886,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1959,7 +1992,7 @@ int discard_index(struct index_state *istate)
 		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
 		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
 			continue;
-		free(istate->cache[i]);
+		discard_cache_entry(istate->cache[i]);
 	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2649,14 +2682,13 @@ int read_index_unmerged(struct index_state *istate)
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i];
 		struct cache_entry *new_ce;
-		int size, len;
+		int len;
 
 		if (!ce_stage(ce))
 			continue;
 		unmerged = 1;
 		len = ce_namelen(ce);
-		size = cache_entry_size(len);
-		new_ce = xcalloc(1, size);
+		new_ce = make_empty_cache_entry(istate, len);
 		memcpy(new_ce->name, ce->name, len);
 		new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
 		new_ce->ce_namelen = len;
@@ -2765,3 +2797,8 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	dst->untracked = src->untracked;
 	src->untracked = NULL;
 }
+
+void discard_cache_entry(struct cache_entry *ce)
+{
+	free(ce);
+}
diff --git a/resolve-undo.c b/resolve-undo.c
index 4d4e5cb6bf..c30ae5cf49 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,7 +146,9 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], &ru->oid[i],
+		nce = make_cache_entry(istate,
+				       ru->mode[i],
+				       &ru->oid[i],
 				       name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
diff --git a/split-index.c b/split-index.c
index 660c75f31f..317900db8b 100644
--- a/split-index.c
+++ b/split-index.c
@@ -123,7 +123,7 @@ static void replace_entry(size_t pos, void *data)
 	src->ce_flags |= CE_UPDATE_IN_BASE;
 	src->ce_namelen = dst->ce_namelen;
 	copy_cache_entry(dst, src);
-	free(src);
+	discard_cache_entry(src);
 	si->nr_replacements++;
 }
 
@@ -224,7 +224,7 @@ void prepare_to_write_split_index(struct index_state *istate)
 			base->ce_flags = base_flags;
 			if (ret)
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
-			free(base);
+			discard_cache_entry(base);
 			si->base->cache[ce->index - 1] = ce;
 		}
 		for (i = 0; i < si->base->cache_nr; i++) {
@@ -301,7 +301,7 @@ void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce
 	    ce == istate->split_index->base->cache[ce->index - 1])
 		ce->ce_flags |= CE_REMOVE;
 	else
-		free(ce);
+		discard_cache_entry(ce);
 }
 
 void replace_index_entry_in_base(struct index_state *istate,
@@ -314,7 +314,7 @@ void replace_index_entry_in_base(struct index_state *istate,
 	    old_entry->index <= istate->split_index->base->cache_nr) {
 		new_entry->index = old_entry->index;
 		if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
-			free(istate->split_index->base->cache[new_entry->index - 1]);
+			discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
 		istate->split_index->base->cache[new_entry->index - 1] = new_entry;
 	}
 }
diff --git a/tree.c b/tree.c
index 2c9c49725c..7bbf304f9f 100644
--- a/tree.c
+++ b/tree.c
@@ -17,15 +17,13 @@ static int read_one_entry_opt(struct index_state *istate,
 			      unsigned mode, int stage, int opt)
 {
 	int len;
-	unsigned int size;
 	struct cache_entry *ce;
 
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 
 	len = strlen(pathname);
-	size = cache_entry_size(baselen + len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, baselen + len);
 
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(stage);
diff --git a/unpack-trees.c b/unpack-trees.c
index 3a85a02a77..33cba550b0 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -203,10 +203,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce)
+static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
 {
 	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = xmalloc(size);
+	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
 
 	memcpy(new_entry, ce, size);
 	return new_entry;
@@ -216,7 +216,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce), set, clear);
+	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -797,10 +797,17 @@ static int ce_in_traverse_path(const struct cache_entry *ce,
 	return (info->pathlen < ce_namelen(ce));
 }
 
-static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
+static struct cache_entry *create_ce_entry(const struct traverse_info *info,
+	const struct name_entry *n,
+	int stage,
+	struct index_state *istate,
+	int is_transient)
 {
 	int len = traverse_path_len(info, n);
-	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
+	struct cache_entry *ce =
+		is_transient ?
+		make_empty_transient_cache_entry(len) :
+		make_empty_cache_entry(istate, len);
 
 	ce->ce_mode = create_ce_mode(n->mode);
 	ce->ce_flags = create_ce_flags(stage);
@@ -846,7 +853,15 @@ static int unpack_nondirectories(int n, unsigned long mask,
 			stage = 3;
 		else
 			stage = 2;
-		src[i + o->merge] = create_ce_entry(info, names + i, stage);
+
+		/*
+		 * If the merge bit is set, then the cache entries are
+		 * discarded in the following block.  In this case,
+		 * construct "transient" cache_entries, as they are
+		 * not stored in the index.  otherwise construct the
+		 * cache entry from the index aware logic.
+		 */
+		src[i + o->merge] = create_ce_entry(info, names + i, stage, &o->result, o->merge);
 	}
 
 	if (o->merge) {
@@ -855,7 +870,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		for (i = 0; i < n; i++) {
 			struct cache_entry *ce = src[i + o->merge];
 			if (ce != o->df_conflict_entry)
-				free(ce);
+				discard_cache_entry(ce);
 		}
 		return rc;
 	}
@@ -1787,7 +1802,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce);
+	struct cache_entry *merge = dup_entry(ce, &o->result);
 
 	if (!old) {
 		/*
@@ -1807,7 +1822,7 @@ static int merged_entry(const struct cache_entry *ce,
 
 		if (verify_absent(merge,
 				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
-			free(merge);
+			discard_cache_entry(merge);
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
@@ -1833,7 +1848,7 @@ static int merged_entry(const struct cache_entry *ce,
 			update = 0;
 		} else {
 			if (verify_uptodate(old, o)) {
-				free(merge);
+				discard_cache_entry(merge);
 				return -1;
 			}
 			/* Migrate old flags over */
-- 
2.17.1

Re: [PATCH v5 3/8] block alloc: add lifecycle APIs for cache_entry structs

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> Add an API around managing the lifetime of cache_entry
> structs. Abstracting memory management details behind this API will
> allow for alternative memory management strategies without affecting
> all the call sites.  This commit does not change how memory is
> allocated or freed. A later commit in this series will allocate cache
> entries from memory pools as appropriate.
>
> Motivation:
> It has been observed that the time spent loading an index with a large
> number of entries is partly dominated by malloc() calls. This change
> is in preparation for using memory pools to reduce the number of
> malloc() calls made when loading an index.

Not worth a reroll, but having these four lines at the very
beginning, dropping the line "Motivation:", and then following that
with "Add an API around ..." as the second paragraph, would make the
above easier to read, without stutter-causing "Motivation:" in the
middle.

> diff --git a/apply.c b/apply.c
> index 8ef975a32d..8a4a4439bc 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -4092,12 +4092,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
>  			return error(_("sha1 information is lacking or useless "
>  				       "(%s)."), name);
>  
> -		ce = make_cache_entry(patch->old_mode, &oid, name, 0, 0);
> +		ce = make_cache_entry(&result, patch->old_mode, &oid, name, 0, 0);
>  		if (!ce)
>  			return error(_("make_cache_entry failed for path '%s'"),
>  				     name);
>  		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
> -			free(ce);
> +			discard_cache_entry(ce);
>  			return error(_("could not add %s to temporary index"),
>  				     name);
>  		}

So..., even though it wasn't clear in the proposed log message, two
large part of the lifecycle management API is (1) make_cache_entry()
knows for which istate it is creating the entry and (2) discarding
the entry may not be just a simple matter of free()ing.  Both of
which makes perfect sense, but if the changes are that easily
enumeratable, it would have been nicer for readers if the commit did
so in the proposed log message.

> @@ -4424,27 +4423,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
>  				       struct patch *patch)
>  {
>  	int stage, namelen;
> -	unsigned ce_size, mode;
> +	unsigned mode;
>  	struct cache_entry *ce;
>  
>  	if (!state->update_index)
>  		return 0;
>  	namelen = strlen(patch->new_name);
> -	ce_size = cache_entry_size(namelen);
>  	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
>  
>  	remove_file_from_cache(patch->new_name);
>  	for (stage = 1; stage < 4; stage++) {
>  		if (is_null_oid(&patch->threeway_stage[stage - 1]))
>  			continue;
> -		ce = xcalloc(1, ce_size);
> +		ce = make_empty_cache_entry(&the_index, namelen);

... and another one in the enumeration is make_empty_cache_entry()
which is somehow different.  And the readers are forced to read its
implementation to find out how it is different, but the use of the
same discard_cache_entry() suggests that the liftime rule of an
entry allcoated by it may be similar to those created by
make_cache_entry().

> ...
>  		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
> -			free(ce);
> +			discard_cache_entry(ce);
>  			return error(_("unable to add cache entry for %s"),
>  				     patch->new_name);
>  		}

> @@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
>  	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
>  		die(_("Unable to add merge result for '%s'"), path);
>  	free(result_buf.ptr);
> -	ce = make_cache_entry(mode, &oid, path, 2, 0);
> +	ce = make_transient_cache_entry(mode, &oid, path, 2);

... and then yet another, which is "transient".  An intelligent
reader can guess from the lack of istate parameter (and from the
word "transient") that the resulting one would not belong to any
in-core index.

>  	if (!ce)
>  		die(_("make_cache_entry failed for path '%s'"), path);
>  	status = checkout_entry(ce, state, NULL);
> -	free(ce);
> +	discard_cache_entry(ce);

... but discovers that it is discarded the same way, realizes that
ce knows how it was allocated to allow discard() different way to
discard it, and his/her earlier conjecture about make_empty() does
not hold at all and gets somewhat disappointed.

> diff --git a/cache.h b/cache.h
> index 3fbf24771a..035a627bea 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -339,6 +339,40 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
>  extern void free_name_hash(struct index_state *istate);
>  
>  
> +/* Cache entry creation and cleanup */
> +
> +/*
> + * Create cache_entry intended for use in the specified index. Caller
> + * is responsible for discarding the cache_entry with
> + * `discard_cache_entry`.
> + */
> +struct cache_entry *make_cache_entry(struct index_state *istate,
> +				     unsigned int mode,
> +				     const struct object_id *oid,
> +				     const char *path,
> +				     int stage,
> +				     unsigned int refresh_options);
> +
> +struct cache_entry *make_empty_cache_entry(struct index_state *istate,
> +					   size_t name_len);
> +
> +/*
> + * Create a cache_entry that is not intended to be added to an index.
> + * Caller is responsible for discarding the cache_entry
> + * with `discard_cache_entry`.
> + */
> +struct cache_entry *make_transient_cache_entry(unsigned int mode,
> +					       const struct object_id *oid,
> +					       const char *path,
> +					       int stage);
> +
> +struct cache_entry *make_empty_transient_cache_entry(size_t name_len);

OK, finally it becomes clear that we have per-istate and transient
sets of two (i.e. one that takes the path, stage and mode pfront,
and the other that only takes the length of the name), and ...

> +/*
> + * Discard cache entry.
> + */
> +void discard_cache_entry(struct cache_entry *ce);

... a single function that knows how to discard each kind.  It would
have really helped the reader to talk about them in the proposed log
message, as they are only 5 functions.  Another way to make it easier
for readers would have been to show the diff for cache.h first before
diffs for all the others.

Re: [PATCH v5 3/8] block alloc: add lifecycle APIs for cache_entry structs

[SZEDER Gábor]

> diff --git a/read-cache.c b/read-cache.c
> index 9624ce1784..116fd51680 100644
> --- a/read-cache.c
> +++ b/read-cache.c

> +struct cache_entry *make_transient_cache_entry(unsigned int mode, const struct object_id *oid,
> +					       const char *path, int stage)
> +{
> +	struct cache_entry *ce;
> +	int len;
> +
> +	if (!verify_path(path, mode)) {
> +		error("Invalid path '%s'", path);
> +		return NULL;
> +	}
> +
> +	len = strlen(path);
> +	ce = make_empty_transient_cache_entry(len);
> +
> +	hashcpy(ce->oid.hash, oid->hash);

Please use oidcpy() here, too.

[PATCH v5 4/8] mem-pool: only search head block for available space

[Jameson Miller]

Instead of searching all memory blocks for available space to fulfill
a memory request, only search the head block. If the head block does
not have space, assume that previous block would most likely not be
able to fulfill request either. This could potentially lead to more
memory fragmentation, but also avoids searching memory blocks that
probably will not be able to fulfill request.

This pattern will benefit consumers that are able to generate a good
estimate for how much memory will be needed, or if they are performing
fixed sized allocations, so that once a block is exhausted it will
never be able to fulfill a future request.

The impact of this change on memory was tested by running fast-import on
the git.git and linux.git repositories. The total amount of memory
allocated to the mem-pools did not change with this approach, indicating
that there is not much memory benefit to searching all nodes in the
linked list.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index 389d7af447..c80124f1fe 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -21,16 +21,16 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
-	struct mp_block *p;
+	struct mp_block *p = NULL;
 	void *r;
 
 	/* round up to a 'uintmax_t' alignment */
 	if (len & (sizeof(uintmax_t) - 1))
 		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
 
-	for (p = mem_pool->mp_block; p; p = p->next_block)
-		if (p->end - p->next_free >= len)
-			break;
+	if (mem_pool->mp_block &&
+	    mem_pool->mp_block->end - mem_pool->mp_block->next_free >= len)
+		p = mem_pool->mp_block;
 
 	if (!p) {
 		if (len >= (mem_pool->block_alloc / 2)) {
-- 
2.17.1

[PATCH v5 5/8] mem-pool: add life cycle management functions

[Jameson Miller]

Add initialization and discard functions to mem_pool type. As the
memory allocated by mem_pool can now be freed, we also track the large
allocations.

If the there are existing mp_blocks in the mem_poo's linked list of
mp_blocksl, then the mp_block for a large allocation is inserted
behind the head block. This is because only the head mp_block is considered
when searching for availble space. This results in the following
desirable properties:

1) The mp_block allocated for the large request will not be included
not included in the search for available in future requests, the large
mp_block is sized for the specific request and does not contain any
spare space.

2) The head mp_block will not bumped from considation for future
memory requests just because a request for a large chunk of memory
came in.

These changes are in preparation for a future commit that will utilize
creating and discarding memory pool.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++--------
 mem-pool.h | 10 +++++++++
 2 files changed, 61 insertions(+), 8 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index c80124f1fe..1769400d2d 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -5,20 +5,65 @@
 #include "cache.h"
 #include "mem-pool.h"
 
-static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
+#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
+
+/*
+ * Allocate a new mp_block and insert it after the block specified in
+ * `insert_after`. If `insert_after` is NULL, then insert block at the
+ * head of the linked list.
+ */
+static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc, struct mp_block *insert_after)
 {
 	struct mp_block *p;
 
 	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
 	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
-	p->next_block = mem_pool->mp_block;
+
 	p->next_free = (char *)p->space;
 	p->end = p->next_free + block_alloc;
-	mem_pool->mp_block = p;
+
+	if (insert_after) {
+		p->next_block = insert_after->next_block;
+		insert_after->next_block = p;
+	} else {
+		p->next_block = mem_pool->mp_block;
+		mem_pool->mp_block = p;
+	}
 
 	return p;
 }
 
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
+{
+	struct mem_pool *pool;
+
+	if (*mem_pool)
+		return;
+
+	pool = xcalloc(1, sizeof(*pool));
+
+	pool->block_alloc = BLOCK_GROWTH_SIZE;
+
+	if (initial_size > 0)
+		mem_pool_alloc_block(pool, initial_size, NULL);
+
+	*mem_pool = pool;
+}
+
+void mem_pool_discard(struct mem_pool *mem_pool)
+{
+	struct mp_block *block, *block_to_free;
+
+	while ((block = mem_pool->mp_block))
+	{
+		block_to_free = block;
+		block = block->next_block;
+		free(block_to_free);
+	}
+
+	free(mem_pool);
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p = NULL;
@@ -33,12 +78,10 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 		p = mem_pool->mp_block;
 
 	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2)) {
-			mem_pool->pool_alloc += len;
-			return xmalloc(len);
-		}
+		if (len >= (mem_pool->block_alloc / 2))
+			return mem_pool_alloc_block(mem_pool, len, mem_pool->mp_block);
 
-		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
+		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc, NULL);
 	}
 
 	r = p->next_free;
diff --git a/mem-pool.h b/mem-pool.h
index 829ad58ecf..f75b3365d5 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -21,6 +21,16 @@ struct mem_pool {
 	size_t pool_alloc;
 };
 
+/*
+ * Initialize mem_pool with specified initial size.
+ */
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
+
+/*
+ * Discard a memory pool and free all the memory it is responsible for.
+ */
+void mem_pool_discard(struct mem_pool *mem_pool);
+
 /*
  * Alloc memory from the mem_pool.
  */
-- 
2.17.1

Re: [PATCH v5 5/8] mem-pool: add life cycle management functions

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> Add initialization and discard functions to mem_pool type. As the
> memory allocated by mem_pool can now be freed, we also track the large
> allocations.
>
> If the there are existing mp_blocks in the mem_poo's linked list of

mem_poo?

> mp_blocksl, then the mp_block for a large allocation is inserted

mp_blocksl?

[PATCH v5 6/8] mem-pool: fill out functionality

[Jameson Miller]

Add functions for:

    - combining two memory pools

    - determining if a memory address is within the range managed by a
      memory pool

These functions will be used by future commits.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 mem-pool.h | 13 +++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/mem-pool.c b/mem-pool.c
index 1769400d2d..b250a5fe40 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -96,3 +96,45 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	memset(r, 0, len);
 	return r;
 }
+
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
+{
+	struct mp_block *p;
+
+	/* Check if memory is allocated in a block */
+	for (p = mem_pool->mp_block; p; p = p->next_block)
+		if ((mem >= ((void *)p->space)) &&
+		    (mem < ((void *)p->end)))
+			return 1;
+
+	return 0;
+}
+
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
+{
+	struct mp_block *p;
+
+	/* Append the blocks from src to dst */
+	if (dst->mp_block && src->mp_block) {
+		/*
+		 * src and dst have blocks, append
+		 * blocks from src to dst.
+		 */
+		p = dst->mp_block;
+		while (p->next_block)
+			p = p->next_block;
+
+		p->next_block = src->mp_block;
+	} else if (src->mp_block) {
+		/*
+		 * src has blocks, dst is empty.
+		 */
+		dst->mp_block = src->mp_block;
+	} else {
+		/* src is empty, nothing to do. */
+	}
+
+	dst->pool_alloc += src->pool_alloc;
+	src->pool_alloc = 0;
+	src->mp_block = NULL;
+}
diff --git a/mem-pool.h b/mem-pool.h
index f75b3365d5..adeefdcb28 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -41,4 +41,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
+ * pool will be empty and not contain any memory. It still needs to be free'd
+ * with a call to `mem_pool_discard`.
+ */
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
+
+/*
+ * Check if a memory pointed at by 'mem' is part of the range of
+ * memory managed by the specified mem_pool.
+ */
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
+
 #endif
-- 
2.17.1

Re: [PATCH v5 6/8] mem-pool: fill out functionality

[Junio C Hamano]

Jameson Miller <jamill@microsoft.com> writes:

> +void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
> +{
> +	struct mp_block *p;
> +
> +	/* Append the blocks from src to dst */
> +	if (dst->mp_block && src->mp_block) {
> +		/*
> +		 * src and dst have blocks, append
> +		 * blocks from src to dst.
> +		 */
> +		p = dst->mp_block;
> +		while (p->next_block)
> +			p = p->next_block;
> +
> +		p->next_block = src->mp_block;

Just being curious, but does this interact with the "we carve out
only from the first block" done in step 4/8?  The remaining unused
space in the first block in the src pool would be wasted, which may
not be such a big deal and may not even be worth comparing the
available space in two blocks and picking a larger one.  But we do
want to decide _after_ thinking things through nevertheless.

RE: [PATCH v5 6/8] mem-pool: fill out functionality

[Jameson Miller]

> > +void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src) {
> > +	struct mp_block *p;
> > +
> > +	/* Append the blocks from src to dst */
> > +	if (dst->mp_block && src->mp_block) {
> > +		/*
> > +		 * src and dst have blocks, append
> > +		 * blocks from src to dst.
> > +		 */
> > +		p = dst->mp_block;
> > +		while (p->next_block)
> > +			p = p->next_block;
> > +
> > +		p->next_block = src->mp_block;
> 
> Just being curious, but does this interact with the "we carve out only from the
> first block" done in step 4/8?  The remaining unused space in the first block in
> the src pool would be wasted, which may not be such a big deal and may not
> even be worth comparing the available space in two blocks and picking a larger
> one.  But we do want to decide _after_ thinking things through nevertheless.

Good question - and this is something I had thought about.

In the context of current usage, this function is currently not
used frequently. It is only used in split index with
move_cache_to_base_index and remove_split_index. In either case,
the cache_entries should already be loaded into memory, and I
don't expect a big enough difference in the amount of left over
space to make a meaningful difference.

In the general case I could see this being a bigger case.

For now, I thought the logic as is was an appropriate tradeoff. I
don't think it would be complicated to do something smarter here,
but I also didn't see much benefit in current usage. If we prefer
something else here, I can update this logic.

[PATCH v5 7/8] block alloc: allocate cache entries from mem-pool

[Jameson Miller]

When reading large indexes from disk, a portion of the time is
dominated in malloc() calls. This can be mitigated by allocating a
large block of memory and manage it ourselves via memory pools.

This change moves the cache entry allocation to be on top of memory
pools.

Design:

The index_state struct will gain a notion of an associated memory_pool
from which cache_entries will be allocated from. When reading in the
index from disk, we have information on the number of entries and
their size, which can guide us in deciding how large our initial
memory allocation should be. When an index is discarded, the
associated memory_pool will be discarded as well - so the lifetime of
a cache_entry is tied to the lifetime of the index_state that it was
allocated for.

In the case of a Split Index, the following rules are followed. 1st,
some terminology is defined:

Terminology:
  - 'the_index': represents the logical view of the index

  - 'split_index': represents the "base" cache entries. Read from the
    split index file.

'the_index' can reference a single split_index, as well as
cache_entries from the split_index. `the_index` will be discarded
before the `split_index` is.  This means that when we are allocating
cache_entries in the presence of a split index, we need to allocate
the entries from the `split_index`'s memory pool.  This allows us to
follow the pattern that `the_index` can reference cache_entries from
the `split_index`, and that the cache_entries will not be freed while
they are still being referenced.

Managing transient cache_entry structs:
Cache entries are usually allocated for an index, but this is not always
the case. Cache entries are sometimes allocated because this is the
type that the existing checkout_entry function works with. Because of
this, the existing code needs to handle cache entries associated with an
index / memory pool, and those that only exist transiently. Several
strategies were contemplated around how to handle this:

Chosen approach:
An extra field was added to the cache_entry type to track whether the
cache_entry was allocated from a memory pool or not. This is currently
an int field, as there are no more available bits in the existing
ce_flags bit field. If / when more bits are needed, this new field can
be turned into a proper bit field.

Alternatives:

1) Do not include any information about how the cache_entry was
allocated. Calling code would be responsible for tracking whether the
cache_entry needed to be freed or not.
  Pro: No extra memory overhead to track this state
  Con: Extra complexity in callers to handle this correctly.

The extra complexity and burden to not regress this behavior in the
future was more than we wanted.

2) cache_entry would gain knowledge about which mem_pool allocated it
  Pro: Could (potentially) do extra logic to know when a mem_pool no
       longer had references to any cache_entry
  Con: cache_entry would grow heavier by a pointer, instead of int

We didn't see a tangible benefit to this approach

3) Do not add any extra information to a cache_entry, but when freeing a
   cache entry, check if the memory exists in a region managed by existing
   mem_pools.
  Pro: No extra memory overhead to track state
  Con: Extra computation is performed when freeing cache entries

We decided tracking and iterating over known memory pool regions was
less desirable than adding an extra field to track this stae.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h        |  21 +++++++++
 mem-pool.c     |   3 +-
 read-cache.c   | 119 +++++++++++++++++++++++++++++++++++++++++--------
 split-index.c  |  50 +++++++++++++++++----
 unpack-trees.c |  13 +-----
 5 files changed, 167 insertions(+), 39 deletions(-)

diff --git a/cache.h b/cache.h
index 035a627bea..8fd89ae51f 100644
--- a/cache.h
+++ b/cache.h
@@ -15,6 +15,7 @@
 #include "path.h"
 #include "sha1-array.h"
 #include "repository.h"
+#include "mem-pool.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -156,6 +157,7 @@ struct cache_entry {
 	struct stat_data ce_stat_data;
 	unsigned int ce_mode;
 	unsigned int ce_flags;
+	unsigned int mem_pool_allocated;
 	unsigned int ce_namelen;
 	unsigned int index;	/* for link extension */
 	struct object_id oid;
@@ -227,6 +229,7 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 				    const struct cache_entry *src)
 {
 	unsigned int state = dst->ce_flags & CE_HASHED;
+	int mem_pool_allocated = dst->mem_pool_allocated;
 
 	/* Don't copy hash chain and name */
 	memcpy(&dst->ce_stat_data, &src->ce_stat_data,
@@ -235,6 +238,9 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 
 	/* Restore the hash state */
 	dst->ce_flags = (dst->ce_flags & ~CE_HASHED) | state;
+
+	/* Restore the mem_pool_allocated flag */
+	dst->mem_pool_allocated = mem_pool_allocated;
 }
 
 static inline unsigned create_ce_flags(unsigned stage)
@@ -328,6 +334,7 @@ struct index_state {
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
+	struct mem_pool *ce_mem_pool;
 };
 
 extern struct index_state the_index;
@@ -373,6 +380,20 @@ struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Duplicate a cache_entry. Allocate memory for the new entry from a
+ * memory_pool. Takes into account cache_entry fields that are meant
+ * for managing the underlying memory allocation of the cache_entry.
+ */
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce, struct index_state *istate);
+
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/mem-pool.c b/mem-pool.c
index b250a5fe40..139617cb23 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -54,7 +54,8 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 {
 	struct mp_block *block, *block_to_free;
 
-	while ((block = mem_pool->mp_block))
+	block = mem_pool->mp_block;
+	while (block)
 	{
 		block_to_free = block;
 		block = block->next_block;
diff --git a/read-cache.c b/read-cache.c
index 116fd51680..f346437800 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -46,6 +46,48 @@
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
 		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
+
+/*
+ * This is an estimate of the pathname length in the index.  We use
+ * this for V4 index files to guess the un-deltafied size of the index
+ * in memory because of pathname deltafication.  This is not required
+ * for V2/V3 index formats because their pathnames are not compressed.
+ * If the initial amount of memory set aside is not sufficient, the
+ * mem pool will allocate extra memory.
+ */
+#define CACHE_ENTRY_PATH_LENGTH 80
+
+static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry *ce;
+	ce = mem_pool_alloc(mem_pool, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry * ce;
+	ce = mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static struct mem_pool *find_mem_pool(struct index_state *istate)
+{
+	struct mem_pool **pool_ptr;
+
+	if (istate->split_index && istate->split_index->base)
+		pool_ptr = &istate->split_index->base->ce_mem_pool;
+	else
+		pool_ptr = &istate->ce_mem_pool;
+
+	if (!*pool_ptr)
+		mem_pool_init(pool_ptr, 0);
+
+	return *pool_ptr;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -746,7 +788,7 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 
 struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
 {
-	return xcalloc(1, cache_entry_size(len));
+	return mem_pool__ce_calloc(find_mem_pool(istate), len);
 }
 
 struct cache_entry *make_empty_transient_cache_entry(size_t len)
@@ -1668,13 +1710,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+static struct cache_entry *cache_entry_from_ondisk(struct mem_pool *mem_pool,
 						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = make_empty_cache_entry(istate, len);
+	struct cache_entry *ce = mem_pool__ce_alloc(mem_pool, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1716,7 +1758,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct index_state *istate,
+static struct cache_entry *create_from_disk(struct mem_pool *mem_pool,
 					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
@@ -1748,13 +1790,13 @@ static struct cache_entry *create_from_disk(struct index_state *istate,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags,
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1828,6 +1870,22 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_fsmonitor(istate);
 }
 
+static size_t estimate_cache_size_from_compressed(unsigned int entries)
+{
+	return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_PATH_LENGTH);
+}
+
+static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
+{
+	long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
+
+	/*
+	 * Account for potential alignment differences.
+	 */
+	per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	return ondisk_size + entries * per_entry;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1874,10 +1932,15 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
 	istate->initialized = 1;
 
-	if (istate->version == 4)
+	if (istate->version == 4) {
 		previous_name = &previous_name_buf;
-	else
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size_from_compressed(istate->cache_nr));
+	} else {
 		previous_name = NULL;
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size(mmap_size, istate->cache_nr));
+	}
 
 	src_offset = sizeof(*hdr);
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -1886,7 +1949,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate->ce_mem_pool, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1983,17 +2046,13 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-	int i;
+	/*
+	 * Cache entries in istate->cache[] should have been allocated
+	 * from the memory pool associated with this index, or from an
+	 * associated split_index. There is no need to free individual
+	 * cache entries.
+	 */
 
-	for (i = 0; i < istate->cache_nr; i++) {
-		if (istate->cache[i]->index &&
-		    istate->split_index &&
-		    istate->split_index->base &&
-		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-			continue;
-		discard_cache_entry(istate->cache[i]);
-	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -2007,6 +2066,12 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool);
+		istate->ce_mem_pool = NULL;
+	}
+
 	return 0;
 }
 
@@ -2798,7 +2863,23 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	src->untracked = NULL;
 }
 
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
+				    struct index_state *istate)
+{
+	unsigned int size = ce_size(ce);
+	int mem_pool_allocated;
+	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
+	mem_pool_allocated = new_entry->mem_pool_allocated;
+
+	memcpy(new_entry, ce, size);
+	new_entry->mem_pool_allocated = mem_pool_allocated;
+	return new_entry;
+}
+
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && ce->mem_pool_allocated)
+		return;
+
 	free(ce);
 }
diff --git a/split-index.c b/split-index.c
index 317900db8b..84f067e10d 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,16 +73,31 @@ void move_cache_to_base_index(struct index_state *istate)
 	int i;
 
 	/*
-	 * do not delete old si->base, its index entries may be shared
-	 * with istate->cache[]. Accept a bit of leaking here because
-	 * this code is only used by short-lived update-index.
+	 * If there was a previous base index, then transfer ownership of allocated
+	 * entries to the parent index.
 	 */
+	if (si->base &&
+		si->base->ce_mem_pool) {
+
+		if (!istate->ce_mem_pool)
+			mem_pool_init(&istate->ce_mem_pool, 0);
+
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+	}
+
 	si->base = xcalloc(1, sizeof(*si->base));
 	si->base->version = istate->version;
 	/* zero timestamp disables racy test in ce_write_index() */
 	si->base->timestamp = istate->timestamp;
 	ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
 	si->base->cache_nr = istate->cache_nr;
+
+	/*
+	 * The mem_pool needs to move with the allocated entries.
+	 */
+	si->base->ce_mem_pool = istate->ce_mem_pool;
+	istate->ce_mem_pool = NULL;
+
 	COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
 	mark_base_index_entries(si->base);
 	for (i = 0; i < si->base->cache_nr; i++)
@@ -331,12 +346,31 @@ void remove_split_index(struct index_state *istate)
 {
 	if (istate->split_index) {
 		/*
-		 * can't discard_split_index(&the_index); because that
-		 * will destroy split_index->base->cache[], which may
-		 * be shared with the_index.cache[]. So yeah we're
-		 * leaking a bit here.
+		 * When removing the split index, we need to move
+		 * ownership of the mem_pool associated with the
+		 * base index to the main index. There may be cache entries
+		 * allocated from the base's memory pool that are shared with
+		 * the_index.cache[].
 		 */
-		istate->split_index = NULL;
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+
+		/*
+		 * The split index no longer owns the mem_pool backing
+		 * its cache array. As we are discarding this index,
+		 * mark the index as having no cache entries, so it
+		 * will not attempt to clean up the cache entries or
+		 * validate them.
+		 */
+		if (istate->split_index->base)
+			istate->split_index->base->cache_nr = 0;
+
+		/*
+		 * We can discard the split index because its
+		 * memory pool has been incorporated into the
+		 * memory pool associated with the the_index.
+		 */
+		discard_split_index(istate);
+
 		istate->cache_changed |= SOMETHING_CHANGED;
 	}
 }
diff --git a/unpack-trees.c b/unpack-trees.c
index 33cba550b0..a3b5131732 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -203,20 +203,11 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
-{
-	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
-
-	memcpy(new_entry, ce, size);
-	return new_entry;
-}
-
 static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
+	do_add_entry(o, dup_cache_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -1802,7 +1793,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce, &o->result);
+	struct cache_entry *merge = dup_cache_entry(ce, &o->result);
 
 	if (!old) {
 		/*
-- 
2.17.1

[PATCH v5 8/8] block alloc: add validations around cache_entry lifecyle

[Jameson Miller]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h      |  6 ++++++
 git.c        |  3 +++
 mem-pool.c   |  6 +++++-
 mem-pool.h   |  2 +-
 read-cache.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 5 files changed, 68 insertions(+), 4 deletions(-)

diff --git a/cache.h b/cache.h
index 8fd89ae51f..b3faef3efc 100644
--- a/cache.h
+++ b/cache.h
@@ -380,6 +380,12 @@ struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Check configuration if we should perform extra validation on cache
+ * entries.
+ */
+int should_validate_cache_entries(void);
+
 /*
  * Duplicate a cache_entry. Allocate memory for the new entry from a
  * memory_pool. Takes into account cache_entry fields that are meant
diff --git a/git.c b/git.c
index 9dbe6ffaa7..c7e4f0351a 100644
--- a/git.c
+++ b/git.c
@@ -414,7 +414,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index 139617cb23..a2841a4a9a 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -50,7 +50,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
 	*mem_pool = pool;
 }
 
-void mem_pool_discard(struct mem_pool *mem_pool)
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory)
 {
 	struct mp_block *block, *block_to_free;
 
@@ -59,6 +59,10 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 	{
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
diff --git a/mem-pool.h b/mem-pool.h
index adeefdcb28..999d3c3a52 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -29,7 +29,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
 /*
  * Discard a memory pool and free all the memory it is responsible for.
  */
-void mem_pool_discard(struct mem_pool *mem_pool);
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory);
 
 /*
  * Alloc memory from the mem_pool.
diff --git a/read-cache.c b/read-cache.c
index f346437800..ba31e929e8 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2050,8 +2050,10 @@ int discard_index(struct index_state *istate)
 	 * Cache entries in istate->cache[] should have been allocated
 	 * from the memory pool associated with this index, or from an
 	 * associated split_index. There is no need to free individual
-	 * cache entries.
+	 * cache entries. validate_cache_entries can detect when this
+	 * assertion does not hold.
 	 */
+	validate_cache_entries(istate);
 
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2068,13 +2070,45 @@ int discard_index(struct index_state *istate)
 	istate->untracked = NULL;
 
 	if (istate->ce_mem_pool) {
-		mem_pool_discard(istate->ce_mem_pool);
+		mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
 		istate->ce_mem_pool = NULL;
 	}
 
 	return 0;
 }
 
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+
+	if (!should_validate_cache_entries() ||!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2878,8 +2912,25 @@ struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
 
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && should_validate_cache_entries())
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
+
 	if (ce && ce->mem_pool_allocated)
 		return;
 
 	free(ce);
 }
+
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
-- 
2.17.1

[PATCH v6 0/8] Allocate cache entries from mem_pool

[Jameson Miller]

Changes since v5:
  - Updated commit messages for:
    7581156e8a read-cache: teach refresh_cache_entry to take istate
    2c962aa0cd block alloc: add lifecycle APIs for cache_entry structs

  - Use oidcpy function instead of hashcpy function

### Interdiff (v5..v6):

diff --git a/read-cache.c b/read-cache.c
index ba31e929e8..fd67e2e8a4 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -814,7 +814,7 @@ struct cache_entry *make_cache_entry(struct index_state *istate,
 	len = strlen(path);
 	ce = make_empty_cache_entry(istate, len);
 
-	hashcpy(ce->oid.hash, oid->hash);
+	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(stage);
 	ce->ce_namelen = len;
@@ -840,7 +840,7 @@ struct cache_entry *make_transient_cache_entry(unsigned int mode, const struct o
 	len = strlen(path);
 	ce = make_empty_transient_cache_entry(len);
 
-	hashcpy(ce->oid.hash, oid->hash);
+	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(stage);
 	ce->ce_namelen = len;


### Patches

Jameson Miller (8):
  read-cache: teach refresh_cache_entry to take istate
  read-cache: teach make_cache_entry to take object_id
  block alloc: add lifecycle APIs for cache_entry structs
  mem-pool: only search head block for available space
  mem-pool: add life cycle management functions
  mem-pool: fill out functionality
  block alloc: allocate cache entries from mem_pool
  block alloc: add validations around cache_entry lifecyle

 apply.c                |  24 ++--
 blame.c                |   5 +-
 builtin/checkout.c     |   8 +-
 builtin/difftool.c     |   6 +-
 builtin/reset.c        |   2 +-
 builtin/update-index.c |  26 ++--
 cache.h                |  64 +++++++++-
 git.c                  |   3 +
 mem-pool.c             | 114 ++++++++++++++++--
 mem-pool.h             |  23 ++++
 merge-recursive.c      |   4 +-
 read-cache.c           | 264 ++++++++++++++++++++++++++++++++++-------
 resolve-undo.c         |   4 +-
 split-index.c          |  58 +++++++--
 tree.c                 |   4 +-
 unpack-trees.c         |  40 ++++---
 16 files changed, 515 insertions(+), 134 deletions(-)


base-commit: ed843436dd4924c10669820cc73daf50f0b4dabd
-- 
2.17.1

[PATCH v6 1/8] read-cache: teach refresh_cache_entry to take istate

[Jameson Miller]

Refactor refresh_cache_entry() to work on a specific index, instead of
implicitly using the_index. This is in preparation for making the
make_cache_entry function apply to a specific index.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h           | 2 +-
 merge-recursive.c | 2 +-
 read-cache.c      | 9 +++++----
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/cache.h b/cache.h
index d49092d94d..93af25f586 100644
--- a/cache.h
+++ b/cache.h
@@ -751,7 +751,7 @@ extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 #define REFRESH_IGNORE_SUBMODULES	0x0010	/* ignore submodules */
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 extern int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
-extern struct cache_entry *refresh_cache_entry(struct cache_entry *, unsigned int);
+extern struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 /*
  * Opportunistically update the index but do not complain if we can't.
diff --git a/merge-recursive.c b/merge-recursive.c
index bed4a5be02..8b3d6781c7 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -326,7 +326,7 @@ static int add_cacheinfo(struct merge_options *o,
 	if (refresh) {
 		struct cache_entry *nce;
 
-		nce = refresh_cache_entry(ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
+		nce = refresh_cache_entry(&the_index, ce, CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
 		if (!nce)
 			return err(o, _("add_cacheinfo failed to refresh for path '%s'; merge aborting."), path);
 		if (nce != ce)
diff --git a/read-cache.c b/read-cache.c
index 372588260e..fa8366ecab 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -767,7 +767,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	ce->ce_namelen = len;
 	ce->ce_mode = create_ce_mode(mode);
 
-	ret = refresh_cache_entry(ce, refresh_options);
+	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
 		free(ce);
 	return ret;
@@ -1473,10 +1473,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	return has_errors;
 }
 
-struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
-					       unsigned int options)
+struct cache_entry *refresh_cache_entry(struct index_state *istate,
+					struct cache_entry *ce,
+					unsigned int options)
 {
-	return refresh_cache_ent(&the_index, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL);
 }
 
 
-- 
2.17.1

[PATCH v6 2/8] read-cache: teach make_cache_entry to take object_id

[Jameson Miller]

Teach make_cache_entry function to take object_id instead of a SHA-1.
---
 apply.c            | 2 +-
 builtin/checkout.c | 2 +-
 builtin/difftool.c | 4 ++--
 builtin/reset.c    | 2 +-
 cache.h            | 7 ++++++-
 merge-recursive.c  | 2 +-
 read-cache.c       | 8 +++++---
 resolve-undo.c     | 2 +-
 8 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/apply.c b/apply.c
index 959c457910..8ef975a32d 100644
--- a/apply.c
+++ b/apply.c
@@ -4092,7 +4092,7 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, oid.hash, name, 0, 0);
+		ce = make_cache_entry(patch->old_mode, &oid, name, 0, 0);
 		if (!ce)
 			return error(_("make_cache_entry failed for path '%s'"),
 				     name);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 2e1d2376d2..548bf40f25 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -230,7 +230,7 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+	ce = make_cache_entry(mode, &oid, path, 2, 0);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
diff --git a/builtin/difftool.c b/builtin/difftool.c
index bc97d4aef2..873a06f0d9 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,7 +321,7 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid->hash, path, 0, 0);
+	ce = make_cache_entry(mode, oid, path, 0, 0);
 	ret = checkout_entry(ce, state, NULL);
 
 	free(ce);
@@ -488,7 +488,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
+					make_cache_entry(rmode, &roid,
 							 dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
diff --git a/builtin/reset.c b/builtin/reset.c
index a862c70fab..00109b041f 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,7 +134,7 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, one->oid.hash, one->path,
+		ce = make_cache_entry(one->mode, &one->oid, one->path,
 				      0, 0);
 		if (!ce)
 			die(_("make_cache_entry failed for path '%s'"),
diff --git a/cache.h b/cache.h
index 93af25f586..3fbf24771a 100644
--- a/cache.h
+++ b/cache.h
@@ -698,7 +698,12 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, unsigned int refresh_options);
+extern struct cache_entry *make_cache_entry(unsigned int mode,
+					    const struct object_id *oid,
+					    const char *path,
+					    int stage,
+					    unsigned int refresh_options);
+
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 8b3d6781c7..873321e5c2 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -318,7 +318,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid->hash : null_sha1, path, stage, 0);
+	ce = make_cache_entry(mode, oid ? oid : &null_oid, path, stage, 0);
 	if (!ce)
 		return err(o, _("add_cacheinfo failed for path '%s'; merge aborting."), path);
 
diff --git a/read-cache.c b/read-cache.c
index fa8366ecab..c12664c789 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -746,8 +746,10 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 }
 
 struct cache_entry *make_cache_entry(unsigned int mode,
-		const unsigned char *sha1, const char *path, int stage,
-		unsigned int refresh_options)
+				     const struct object_id *oid,
+				     const char *path,
+				     int stage,
+				     unsigned int refresh_options)
 {
 	int size, len;
 	struct cache_entry *ce, *ret;
@@ -761,7 +763,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	size = cache_entry_size(len);
 	ce = xcalloc(1, size);
 
-	hashcpy(ce->oid.hash, sha1);
+	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(stage);
 	ce->ce_namelen = len;
diff --git a/resolve-undo.c b/resolve-undo.c
index fc5b3b83d9..4d4e5cb6bf 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,7 +146,7 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], ru->oid[i].hash,
+		nce = make_cache_entry(ru->mode[i], &ru->oid[i],
 				       name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
-- 
2.17.1

Re: [PATCH v6 2/8] read-cache: teach make_cache_entry to take object_id

[Stefan Beller]

On Mon, Jul 2, 2018 at 12:49 PM Jameson Miller <jamill@microsoft.com> wrote:
>
> Teach make_cache_entry function to take object_id instead of a SHA-1.

This repeats the subject line?

Sign off missing.

RE: [PATCH v6 2/8] read-cache: teach make_cache_entry to take object_id

[Jameson Miller]

> >
> > Teach make_cache_entry function to take object_id instead of a SHA-1.
> 
> This repeats the subject line?
> 
> Sign off missing.

Thank you Stefan for pointing this out. This does not add much information to the subject line. I could clean it up if I re-roll to fix up the missing sign off.

Junio - would you like me to re-roll this patch series and include the correct sign off, or would you be able to correct this? I can do whichever is easiest for you.

[PATCH v6 3/8] block alloc: add lifecycle APIs for cache_entry structs

[Jameson Miller]

It has been observed that the time spent loading an index with a large
number of entries is partly dominated by malloc() calls. This change
is in preparation for using memory pools to reduce the number of
malloc() calls made to allocate cahce entries when loading an index.

Add an API to allocate and discard cache entries, abstracting the
details of managing the memory backing the cache entries. This commit
does actually change how memory is managed - this will be done in a
later commit in the series.

This change makes the distinction between cache entries that are
associated with an index and cache entries that are not associated with
an index. A main use of cache entries is with an index, and we can
optimize the memory management around this. We still have other cases
where a cache entry is not persisted with an index, and so we need to
handle the "transient" use case as well.

To keep the congnitive overhead of managing the cache entries, there
will only be a single discard function. This means there must be enough
information kept with the cache entry so that we know how to discard
them.

A summary of the main functions in the API is:

make_cache_entry: create cache entry for use in an index. Uses specified
                  parameters to populate cache_entry fields.

make_empty_cache_entry: Create an empty cache entry for use in an index.
                        Returns cache entry with empty fields.

make_transient_cache_entry: create cache entry that is not used in an
                            index. Uses specified parameters to populate
                            cache_entry fields.

make_empty_transient_cache_entry: create cache entry that is not used in
                                  an index. Returns cache entry with
                                  empty fields.

discard_cache_entry: A single function that knows how to discard a cache
                     entry regardless of how it was allocated.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 apply.c                | 24 +++++------
 blame.c                |  5 +--
 builtin/checkout.c     |  8 ++--
 builtin/difftool.c     |  6 +--
 builtin/reset.c        |  2 +-
 builtin/update-index.c | 26 +++++-------
 cache.h                | 40 +++++++++++++++---
 merge-recursive.c      |  2 +-
 read-cache.c           | 93 +++++++++++++++++++++++++++++-------------
 resolve-undo.c         |  4 +-
 split-index.c          |  8 ++--
 tree.c                 |  4 +-
 unpack-trees.c         | 35 +++++++++++-----
 13 files changed, 165 insertions(+), 92 deletions(-)

diff --git a/apply.c b/apply.c
index 8ef975a32d..8a4a4439bc 100644
--- a/apply.c
+++ b/apply.c
@@ -4092,12 +4092,12 @@ static int build_fake_ancestor(struct apply_state *state, struct patch *list)
 			return error(_("sha1 information is lacking or useless "
 				       "(%s)."), name);
 
-		ce = make_cache_entry(patch->old_mode, &oid, name, 0, 0);
+		ce = make_cache_entry(&result, patch->old_mode, &oid, name, 0, 0);
 		if (!ce)
 			return error(_("make_cache_entry failed for path '%s'"),
 				     name);
 		if (add_index_entry(&result, ce, ADD_CACHE_OK_TO_ADD)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("could not add %s to temporary index"),
 				     name);
 		}
@@ -4265,9 +4265,8 @@ static int add_index_file(struct apply_state *state,
 	struct stat st;
 	struct cache_entry *ce;
 	int namelen = strlen(path);
-	unsigned ce_size = cache_entry_size(namelen);
 
-	ce = xcalloc(1, ce_size);
+	ce = make_empty_cache_entry(&the_index, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(0);
@@ -4280,13 +4279,13 @@ static int add_index_file(struct apply_state *state,
 
 		if (!skip_prefix(buf, "Subproject commit ", &s) ||
 		    get_oid_hex(s, &ce->oid)) {
-			free(ce);
-		       return error(_("corrupt patch for submodule %s"), path);
+			discard_cache_entry(ce);
+			return error(_("corrupt patch for submodule %s"), path);
 		}
 	} else {
 		if (!state->cached) {
 			if (lstat(path, &st) < 0) {
-				free(ce);
+				discard_cache_entry(ce);
 				return error_errno(_("unable to stat newly "
 						     "created file '%s'"),
 						   path);
@@ -4294,13 +4293,13 @@ static int add_index_file(struct apply_state *state,
 			fill_stat_cache_info(ce, &st);
 		}
 		if (write_object_file(buf, size, blob_type, &ce->oid) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to create backing store "
 				       "for newly created file %s"), path);
 		}
 	}
 	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error(_("unable to add cache entry for %s"), path);
 	}
 
@@ -4424,27 +4423,26 @@ static int add_conflicted_stages_file(struct apply_state *state,
 				       struct patch *patch)
 {
 	int stage, namelen;
-	unsigned ce_size, mode;
+	unsigned mode;
 	struct cache_entry *ce;
 
 	if (!state->update_index)
 		return 0;
 	namelen = strlen(patch->new_name);
-	ce_size = cache_entry_size(namelen);
 	mode = patch->new_mode ? patch->new_mode : (S_IFREG | 0644);
 
 	remove_file_from_cache(patch->new_name);
 	for (stage = 1; stage < 4; stage++) {
 		if (is_null_oid(&patch->threeway_stage[stage - 1]))
 			continue;
-		ce = xcalloc(1, ce_size);
+		ce = make_empty_cache_entry(&the_index, namelen);
 		memcpy(ce->name, patch->new_name, namelen);
 		ce->ce_mode = create_ce_mode(mode);
 		ce->ce_flags = create_ce_flags(stage);
 		ce->ce_namelen = namelen;
 		oidcpy(&ce->oid, &patch->threeway_stage[stage - 1]);
 		if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error(_("unable to add cache entry for %s"),
 				     patch->new_name);
 		}
diff --git a/blame.c b/blame.c
index a5c9bd78ab..87dade745c 100644
--- a/blame.c
+++ b/blame.c
@@ -173,7 +173,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
 	time_t now;
-	int size, len;
+	int len;
 	struct cache_entry *ce;
 	unsigned mode;
 	struct strbuf msg = STRBUF_INIT;
@@ -271,8 +271,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 			/* Let's not bother reading from HEAD tree */
 			mode = S_IFREG | 0644;
 	}
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, &origin->blob_oid);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 548bf40f25..56d1e1a28d 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -77,7 +77,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		return READ_TREE_RECURSIVE;
 
 	len = base->len + strlen(pathname);
-	ce = xcalloc(1, cache_entry_size(len));
+	ce = make_empty_cache_entry(&the_index, len);
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
@@ -96,7 +96,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 		if (ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
@@ -230,11 +230,11 @@ static int checkout_merged(int pos, const struct checkout *state)
 	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
 		die(_("Unable to add merge result for '%s'"), path);
 	free(result_buf.ptr);
-	ce = make_cache_entry(mode, &oid, path, 2, 0);
+	ce = make_transient_cache_entry(mode, &oid, path, 2);
 	if (!ce)
 		die(_("make_cache_entry failed for path '%s'"), path);
 	status = checkout_entry(ce, state, NULL);
-	free(ce);
+	discard_cache_entry(ce);
 	return status;
 }
 
diff --git a/builtin/difftool.c b/builtin/difftool.c
index 873a06f0d9..4593f0c2cd 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -321,10 +321,10 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid, path, 0, 0);
+	ce = make_transient_cache_entry(mode, oid, path, 0);
 	ret = checkout_entry(ce, state, NULL);
 
-	free(ce);
+	discard_cache_entry(ce);
 	return ret;
 }
 
@@ -488,7 +488,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				 * index.
 				 */
 				struct cache_entry *ce2 =
-					make_cache_entry(rmode, &roid,
+					make_cache_entry(&wtindex, rmode, &roid,
 							 dst_path, 0, 0);
 
 				add_index_entry(&wtindex, ce2,
diff --git a/builtin/reset.c b/builtin/reset.c
index 00109b041f..c3f0cfa1e8 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -134,7 +134,7 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 			continue;
 		}
 
-		ce = make_cache_entry(one->mode, &one->oid, one->path,
+		ce = make_cache_entry(&the_index, one->mode, &one->oid, one->path,
 				      0, 0);
 		if (!ce)
 			die(_("make_cache_entry failed for path '%s'"),
diff --git a/builtin/update-index.c b/builtin/update-index.c
index a8709a26ec..ea2f2a476c 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -268,15 +268,14 @@ static int process_lstat_error(const char *path, int err)
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)
 {
-	int option, size;
+	int option;
 	struct cache_entry *ce;
 
 	/* Was the old index entry already up-to-date? */
 	if (old && !ce_stage(old) && !ce_match_stat(old, st, 0))
 		return 0;
 
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 	memcpy(ce->name, path, len);
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
@@ -285,13 +284,13 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 
 	if (index_path(&ce->oid, path, st,
 		       info_only ? 0 : HASH_WRITE_OBJECT)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return -1;
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
 	if (add_cache_entry(ce, option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
 	}
 	return 0;
@@ -402,15 +401,14 @@ static int process_path(const char *path, struct stat *st, int stat_errno)
 static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 			 const char *path, int stage)
 {
-	int size, len, option;
+	int len, option;
 	struct cache_entry *ce;
 
 	if (!verify_path(path, mode))
 		return error("Invalid path '%s'", path);
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -599,7 +597,6 @@ static struct cache_entry *read_one_ent(const char *which,
 {
 	unsigned mode;
 	struct object_id oid;
-	int size;
 	struct cache_entry *ce;
 
 	if (get_tree_entry(ent, path, &oid, &mode)) {
@@ -612,8 +609,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(&the_index, namelen);
 
 	oidcpy(&ce->oid, &oid);
 	memcpy(ce->name, path, namelen);
@@ -690,8 +686,8 @@ static int unresolve_one(const char *path)
 	error("%s: cannot add their version to the index.", path);
 	ret = -1;
  free_return:
-	free(ce_2);
-	free(ce_3);
+	discard_cache_entry(ce_2);
+	discard_cache_entry(ce_3);
 	return ret;
 }
 
@@ -758,7 +754,7 @@ static int do_reupdate(int ac, const char **av,
 					   ce->name, ce_namelen(ce), 0);
 		if (old && ce->ce_mode == old->ce_mode &&
 		    !oidcmp(&ce->oid, &old->oid)) {
-			free(old);
+			discard_cache_entry(old);
 			continue; /* unchanged */
 		}
 		/* Be careful.  The working tree may not have the
@@ -769,7 +765,7 @@ static int do_reupdate(int ac, const char **av,
 		path = xstrdup(ce->name);
 		update_one(path);
 		free(path);
-		free(old);
+		discard_cache_entry(old);
 		if (save_nr != active_nr)
 			goto redo;
 	}
diff --git a/cache.h b/cache.h
index 3fbf24771a..035a627bea 100644
--- a/cache.h
+++ b/cache.h
@@ -339,6 +339,40 @@ extern void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 extern void free_name_hash(struct index_state *istate);
 
 
+/* Cache entry creation and cleanup */
+
+/*
+ * Create cache_entry intended for use in the specified index. Caller
+ * is responsible for discarding the cache_entry with
+ * `discard_cache_entry`.
+ */
+struct cache_entry *make_cache_entry(struct index_state *istate,
+				     unsigned int mode,
+				     const struct object_id *oid,
+				     const char *path,
+				     int stage,
+				     unsigned int refresh_options);
+
+struct cache_entry *make_empty_cache_entry(struct index_state *istate,
+					   size_t name_len);
+
+/*
+ * Create a cache_entry that is not intended to be added to an index.
+ * Caller is responsible for discarding the cache_entry
+ * with `discard_cache_entry`.
+ */
+struct cache_entry *make_transient_cache_entry(unsigned int mode,
+					       const struct object_id *oid,
+					       const char *path,
+					       int stage);
+
+struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
+
+/*
+ * Discard cache entry.
+ */
+void discard_cache_entry(struct cache_entry *ce);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
@@ -698,12 +732,6 @@ extern int remove_file_from_index(struct index_state *, const char *path);
 extern int add_to_index(struct index_state *, const char *path, struct stat *, int flags);
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 
-extern struct cache_entry *make_cache_entry(unsigned int mode,
-					    const struct object_id *oid,
-					    const char *path,
-					    int stage,
-					    unsigned int refresh_options);
-
 extern int chmod_index_entry(struct index_state *, struct cache_entry *ce, char flip);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
 extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
diff --git a/merge-recursive.c b/merge-recursive.c
index 873321e5c2..06d77afbeb 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -318,7 +318,7 @@ static int add_cacheinfo(struct merge_options *o,
 	struct cache_entry *ce;
 	int ret;
 
-	ce = make_cache_entry(mode, oid ? oid : &null_oid, path, stage, 0);
+	ce = make_cache_entry(&the_index, mode, oid ? oid : &null_oid, path, stage, 0);
 	if (!ce)
 		return err(o, _("add_cacheinfo failed for path '%s'; merge aborting."), path);
 
diff --git a/read-cache.c b/read-cache.c
index c12664c789..41e4d0e67a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -61,7 +61,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 	replace_index_entry_in_base(istate, old, ce);
 	remove_name_hash(istate, old);
-	free(old);
+	discard_cache_entry(old);
 	ce->ce_flags &= ~CE_HASHED;
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
@@ -74,7 +74,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new_entry = xmalloc(cache_entry_size(namelen));
+	new_entry = make_empty_cache_entry(istate, namelen);
 	copy_cache_entry(new_entry, old_entry);
 	new_entry->ce_flags &= ~CE_HASHED;
 	new_entry->ce_namelen = namelen;
@@ -623,7 +623,7 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new_entry = xcalloc(1, cache_entry_size(len));
+	new_entry = make_empty_cache_entry(istate, len);
 	memcpy(new_entry->name, alias->name, len);
 	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
@@ -640,7 +640,7 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
-	int size, namelen, was_same;
+	int namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
@@ -662,8 +662,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
-	size = cache_entry_size(namelen);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, namelen);
 	memcpy(ce->name, path, namelen);
 	ce->ce_namelen = namelen;
 	if (!intent_only)
@@ -704,13 +703,13 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 				ce_mark_uptodate(alias);
 			alias->ce_flags |= CE_ADDED;
 
-			free(ce);
+			discard_cache_entry(ce);
 			return 0;
 		}
 	}
 	if (!intent_only) {
 		if (index_path(&ce->oid, path, st, newflags)) {
-			free(ce);
+			discard_cache_entry(ce);
 			return error("unable to index file %s", path);
 		}
 	} else
@@ -727,9 +726,9 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		    ce->ce_mode == alias->ce_mode);
 
 	if (pretend)
-		free(ce);
+		discard_cache_entry(ce);
 	else if (add_index_entry(istate, ce, add_option)) {
-		free(ce);
+		discard_cache_entry(ce);
 		return error("unable to add %s to index", path);
 	}
 	if (verbose && !was_same)
@@ -745,14 +744,25 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 	return add_to_index(istate, path, &st, flags);
 }
 
-struct cache_entry *make_cache_entry(unsigned int mode,
+struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_empty_transient_cache_entry(size_t len)
+{
+	return xcalloc(1, cache_entry_size(len));
+}
+
+struct cache_entry *make_cache_entry(struct index_state *istate,
+				     unsigned int mode,
 				     const struct object_id *oid,
 				     const char *path,
 				     int stage,
 				     unsigned int refresh_options)
 {
-	int size, len;
 	struct cache_entry *ce, *ret;
+	int len;
 
 	if (!verify_path(path, mode)) {
 		error("Invalid path '%s'", path);
@@ -760,8 +770,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 	}
 
 	len = strlen(path);
-	size = cache_entry_size(len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, len);
 
 	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, path, len);
@@ -771,10 +780,33 @@ struct cache_entry *make_cache_entry(unsigned int mode,
 
 	ret = refresh_cache_entry(&the_index, ce, refresh_options);
 	if (ret != ce)
-		free(ce);
+		discard_cache_entry(ce);
 	return ret;
 }
 
+struct cache_entry *make_transient_cache_entry(unsigned int mode, const struct object_id *oid,
+					       const char *path, int stage)
+{
+	struct cache_entry *ce;
+	int len;
+
+	if (!verify_path(path, mode)) {
+		error("Invalid path '%s'", path);
+		return NULL;
+	}
+
+	len = strlen(path);
+	ce = make_empty_transient_cache_entry(len);
+
+	oidcpy(&ce->oid, oid);
+	memcpy(ce->name, path, len);
+	ce->ce_flags = create_ce_flags(stage);
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	return ce;
+}
+
 /*
  * Chmod an index entry with either +x or -x.
  *
@@ -1270,7 +1302,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 {
 	struct stat st;
 	struct cache_entry *updated;
-	int changed, size;
+	int changed;
 	int refresh = options & CE_MATCH_REFRESH;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
@@ -1350,8 +1382,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
-	size = ce_size(ce);
-	updated = xmalloc(size);
+	updated = make_empty_cache_entry(istate, ce_namelen(ce));
 	copy_cache_entry(updated, ce);
 	memcpy(updated->name, ce->name, ce->ce_namelen + 1);
 	fill_stat_cache_info(updated, &st);
@@ -1637,12 +1668,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = xmalloc(cache_entry_size(len));
+	struct cache_entry *ce = make_empty_cache_entry(istate, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1684,7 +1716,8 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+static struct cache_entry *create_from_disk(struct index_state *istate,
+					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
 {
@@ -1715,13 +1748,13 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(ondisk, flags,
+		ce = cache_entry_from_ondisk(istate, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1853,7 +1886,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1959,7 +1992,7 @@ int discard_index(struct index_state *istate)
 		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
 		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
 			continue;
-		free(istate->cache[i]);
+		discard_cache_entry(istate->cache[i]);
 	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2649,14 +2682,13 @@ int read_index_unmerged(struct index_state *istate)
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i];
 		struct cache_entry *new_ce;
-		int size, len;
+		int len;
 
 		if (!ce_stage(ce))
 			continue;
 		unmerged = 1;
 		len = ce_namelen(ce);
-		size = cache_entry_size(len);
-		new_ce = xcalloc(1, size);
+		new_ce = make_empty_cache_entry(istate, len);
 		memcpy(new_ce->name, ce->name, len);
 		new_ce->ce_flags = create_ce_flags(0) | CE_CONFLICTED;
 		new_ce->ce_namelen = len;
@@ -2765,3 +2797,8 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	dst->untracked = src->untracked;
 	src->untracked = NULL;
 }
+
+void discard_cache_entry(struct cache_entry *ce)
+{
+	free(ce);
+}
diff --git a/resolve-undo.c b/resolve-undo.c
index 4d4e5cb6bf..c30ae5cf49 100644
--- a/resolve-undo.c
+++ b/resolve-undo.c
@@ -146,7 +146,9 @@ int unmerge_index_entry_at(struct index_state *istate, int pos)
 		struct cache_entry *nce;
 		if (!ru->mode[i])
 			continue;
-		nce = make_cache_entry(ru->mode[i], &ru->oid[i],
+		nce = make_cache_entry(istate,
+				       ru->mode[i],
+				       &ru->oid[i],
 				       name, i + 1, 0);
 		if (matched)
 			nce->ce_flags |= CE_MATCHED;
diff --git a/split-index.c b/split-index.c
index 660c75f31f..317900db8b 100644
--- a/split-index.c
+++ b/split-index.c
@@ -123,7 +123,7 @@ static void replace_entry(size_t pos, void *data)
 	src->ce_flags |= CE_UPDATE_IN_BASE;
 	src->ce_namelen = dst->ce_namelen;
 	copy_cache_entry(dst, src);
-	free(src);
+	discard_cache_entry(src);
 	si->nr_replacements++;
 }
 
@@ -224,7 +224,7 @@ void prepare_to_write_split_index(struct index_state *istate)
 			base->ce_flags = base_flags;
 			if (ret)
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
-			free(base);
+			discard_cache_entry(base);
 			si->base->cache[ce->index - 1] = ce;
 		}
 		for (i = 0; i < si->base->cache_nr; i++) {
@@ -301,7 +301,7 @@ void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce
 	    ce == istate->split_index->base->cache[ce->index - 1])
 		ce->ce_flags |= CE_REMOVE;
 	else
-		free(ce);
+		discard_cache_entry(ce);
 }
 
 void replace_index_entry_in_base(struct index_state *istate,
@@ -314,7 +314,7 @@ void replace_index_entry_in_base(struct index_state *istate,
 	    old_entry->index <= istate->split_index->base->cache_nr) {
 		new_entry->index = old_entry->index;
 		if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
-			free(istate->split_index->base->cache[new_entry->index - 1]);
+			discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
 		istate->split_index->base->cache[new_entry->index - 1] = new_entry;
 	}
 }
diff --git a/tree.c b/tree.c
index 2c9c49725c..7bbf304f9f 100644
--- a/tree.c
+++ b/tree.c
@@ -17,15 +17,13 @@ static int read_one_entry_opt(struct index_state *istate,
 			      unsigned mode, int stage, int opt)
 {
 	int len;
-	unsigned int size;
 	struct cache_entry *ce;
 
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 
 	len = strlen(pathname);
-	size = cache_entry_size(baselen + len);
-	ce = xcalloc(1, size);
+	ce = make_empty_cache_entry(istate, baselen + len);
 
 	ce->ce_mode = create_ce_mode(mode);
 	ce->ce_flags = create_ce_flags(stage);
diff --git a/unpack-trees.c b/unpack-trees.c
index 3a85a02a77..33cba550b0 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -203,10 +203,10 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce)
+static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
 {
 	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = xmalloc(size);
+	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
 
 	memcpy(new_entry, ce, size);
 	return new_entry;
@@ -216,7 +216,7 @@ static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce), set, clear);
+	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -797,10 +797,17 @@ static int ce_in_traverse_path(const struct cache_entry *ce,
 	return (info->pathlen < ce_namelen(ce));
 }
 
-static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
+static struct cache_entry *create_ce_entry(const struct traverse_info *info,
+	const struct name_entry *n,
+	int stage,
+	struct index_state *istate,
+	int is_transient)
 {
 	int len = traverse_path_len(info, n);
-	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));
+	struct cache_entry *ce =
+		is_transient ?
+		make_empty_transient_cache_entry(len) :
+		make_empty_cache_entry(istate, len);
 
 	ce->ce_mode = create_ce_mode(n->mode);
 	ce->ce_flags = create_ce_flags(stage);
@@ -846,7 +853,15 @@ static int unpack_nondirectories(int n, unsigned long mask,
 			stage = 3;
 		else
 			stage = 2;
-		src[i + o->merge] = create_ce_entry(info, names + i, stage);
+
+		/*
+		 * If the merge bit is set, then the cache entries are
+		 * discarded in the following block.  In this case,
+		 * construct "transient" cache_entries, as they are
+		 * not stored in the index.  otherwise construct the
+		 * cache entry from the index aware logic.
+		 */
+		src[i + o->merge] = create_ce_entry(info, names + i, stage, &o->result, o->merge);
 	}
 
 	if (o->merge) {
@@ -855,7 +870,7 @@ static int unpack_nondirectories(int n, unsigned long mask,
 		for (i = 0; i < n; i++) {
 			struct cache_entry *ce = src[i + o->merge];
 			if (ce != o->df_conflict_entry)
-				free(ce);
+				discard_cache_entry(ce);
 		}
 		return rc;
 	}
@@ -1787,7 +1802,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce);
+	struct cache_entry *merge = dup_entry(ce, &o->result);
 
 	if (!old) {
 		/*
@@ -1807,7 +1822,7 @@ static int merged_entry(const struct cache_entry *ce,
 
 		if (verify_absent(merge,
 				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
-			free(merge);
+			discard_cache_entry(merge);
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
@@ -1833,7 +1848,7 @@ static int merged_entry(const struct cache_entry *ce,
 			update = 0;
 		} else {
 			if (verify_uptodate(old, o)) {
-				free(merge);
+				discard_cache_entry(merge);
 				return -1;
 			}
 			/* Migrate old flags over */
-- 
2.17.1

Re: [PATCH v6 3/8] block alloc: add lifecycle APIs for cache_entry structs

[Duy Nguyen]

On Mon, Jul 2, 2018 at 9:49 PM Jameson Miller <jamill@microsoft.com> wrote:
> +struct cache_entry *make_transient_cache_entry(unsigned int mode, const struct object_id *oid,
> +                                              const char *path, int stage)
> +{
> +       struct cache_entry *ce;
> +       int len;
> +
> +       if (!verify_path(path, mode)) {
> +               error("Invalid path '%s'", path);

Please wrap all new user-visible strings in _().

> +               return NULL;
> +       }
-- 
Duy

[PATCH v6 4/8] mem-pool: only search head block for available space

[Jameson Miller]

Instead of searching all memory blocks for available space to fulfill
a memory request, only search the head block. If the head block does
not have space, assume that previous block would most likely not be
able to fulfill request either. This could potentially lead to more
memory fragmentation, but also avoids searching memory blocks that
probably will not be able to fulfill request.

This pattern will benefit consumers that are able to generate a good
estimate for how much memory will be needed, or if they are performing
fixed sized allocations, so that once a block is exhausted it will
never be able to fulfill a future request.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index 389d7af447..c80124f1fe 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -21,16 +21,16 @@ static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t b
 
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
-	struct mp_block *p;
+	struct mp_block *p = NULL;
 	void *r;
 
 	/* round up to a 'uintmax_t' alignment */
 	if (len & (sizeof(uintmax_t) - 1))
 		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
 
-	for (p = mem_pool->mp_block; p; p = p->next_block)
-		if (p->end - p->next_free >= len)
-			break;
+	if (mem_pool->mp_block &&
+	    mem_pool->mp_block->end - mem_pool->mp_block->next_free >= len)
+		p = mem_pool->mp_block;
 
 	if (!p) {
 		if (len >= (mem_pool->block_alloc / 2)) {
-- 
2.17.1

[PATCH v6 5/8] mem-pool: add life cycle management functions

[Jameson Miller]

Add initialization and discard functions to mem_pool type. As the
memory allocated by mem_pool can now be freed, we also track the large
allocations.

If the there are existing mp_blocks in the mem_poo's linked list of
mp_blocksl, then the mp_block for a large allocation is inserted
behind the head block. This is because only the head mp_block is considered
when searching for availble space. This results in the following
desirable properties:

1) The mp_block allocated for the large request will not be included
not included in the search for available in future requests, the large
mp_block is sized for the specific request and does not contain any
spare space.

2) The head mp_block will not bumped from considation for future
memory requests just because a request for a large chunk of memory
came in.

These changes are in preparation for a future commit that will utilize
creating and discarding memory pool.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++--------
 mem-pool.h | 10 +++++++++
 2 files changed, 61 insertions(+), 8 deletions(-)

diff --git a/mem-pool.c b/mem-pool.c
index c80124f1fe..1769400d2d 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -5,20 +5,65 @@
 #include "cache.h"
 #include "mem-pool.h"
 
-static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc)
+#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);
+
+/*
+ * Allocate a new mp_block and insert it after the block specified in
+ * `insert_after`. If `insert_after` is NULL, then insert block at the
+ * head of the linked list.
+ */
+static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc, struct mp_block *insert_after)
 {
 	struct mp_block *p;
 
 	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
 	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
-	p->next_block = mem_pool->mp_block;
+
 	p->next_free = (char *)p->space;
 	p->end = p->next_free + block_alloc;
-	mem_pool->mp_block = p;
+
+	if (insert_after) {
+		p->next_block = insert_after->next_block;
+		insert_after->next_block = p;
+	} else {
+		p->next_block = mem_pool->mp_block;
+		mem_pool->mp_block = p;
+	}
 
 	return p;
 }
 
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
+{
+	struct mem_pool *pool;
+
+	if (*mem_pool)
+		return;
+
+	pool = xcalloc(1, sizeof(*pool));
+
+	pool->block_alloc = BLOCK_GROWTH_SIZE;
+
+	if (initial_size > 0)
+		mem_pool_alloc_block(pool, initial_size, NULL);
+
+	*mem_pool = pool;
+}
+
+void mem_pool_discard(struct mem_pool *mem_pool)
+{
+	struct mp_block *block, *block_to_free;
+
+	while ((block = mem_pool->mp_block))
+	{
+		block_to_free = block;
+		block = block->next_block;
+		free(block_to_free);
+	}
+
+	free(mem_pool);
+}
+
 void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 {
 	struct mp_block *p = NULL;
@@ -33,12 +78,10 @@ void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
 		p = mem_pool->mp_block;
 
 	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2)) {
-			mem_pool->pool_alloc += len;
-			return xmalloc(len);
-		}
+		if (len >= (mem_pool->block_alloc / 2))
+			return mem_pool_alloc_block(mem_pool, len, mem_pool->mp_block);
 
-		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc);
+		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc, NULL);
 	}
 
 	r = p->next_free;
diff --git a/mem-pool.h b/mem-pool.h
index 829ad58ecf..f75b3365d5 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -21,6 +21,16 @@ struct mem_pool {
 	size_t pool_alloc;
 };
 
+/*
+ * Initialize mem_pool with specified initial size.
+ */
+void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
+
+/*
+ * Discard a memory pool and free all the memory it is responsible for.
+ */
+void mem_pool_discard(struct mem_pool *mem_pool);
+
 /*
  * Alloc memory from the mem_pool.
  */
-- 
2.17.1

[PATCH v6 6/8] mem-pool: fill out functionality

[Jameson Miller]

Add functions for:

    - combining two memory pools

    - determining if a memory address is within the range managed by a
      memory pool

These functions will be used by future commits.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 mem-pool.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 mem-pool.h | 13 +++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/mem-pool.c b/mem-pool.c
index 1769400d2d..b250a5fe40 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -96,3 +96,45 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	memset(r, 0, len);
 	return r;
 }
+
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
+{
+	struct mp_block *p;
+
+	/* Check if memory is allocated in a block */
+	for (p = mem_pool->mp_block; p; p = p->next_block)
+		if ((mem >= ((void *)p->space)) &&
+		    (mem < ((void *)p->end)))
+			return 1;
+
+	return 0;
+}
+
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src)
+{
+	struct mp_block *p;
+
+	/* Append the blocks from src to dst */
+	if (dst->mp_block && src->mp_block) {
+		/*
+		 * src and dst have blocks, append
+		 * blocks from src to dst.
+		 */
+		p = dst->mp_block;
+		while (p->next_block)
+			p = p->next_block;
+
+		p->next_block = src->mp_block;
+	} else if (src->mp_block) {
+		/*
+		 * src has blocks, dst is empty.
+		 */
+		dst->mp_block = src->mp_block;
+	} else {
+		/* src is empty, nothing to do. */
+	}
+
+	dst->pool_alloc += src->pool_alloc;
+	src->pool_alloc = 0;
+	src->mp_block = NULL;
+}
diff --git a/mem-pool.h b/mem-pool.h
index f75b3365d5..adeefdcb28 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -41,4 +41,17 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
+ * pool will be empty and not contain any memory. It still needs to be free'd
+ * with a call to `mem_pool_discard`.
+ */
+void mem_pool_combine(struct mem_pool *dst, struct mem_pool *src);
+
+/*
+ * Check if a memory pointed at by 'mem' is part of the range of
+ * memory managed by the specified mem_pool.
+ */
+int mem_pool_contains(struct mem_pool *mem_pool, void *mem);
+
 #endif
-- 
2.17.1

[PATCH v6 7/8] block alloc: allocate cache entries from mem_pool

[Jameson Miller]

When reading large indexes from disk, a portion of the time is
dominated in malloc() calls. This can be mitigated by allocating a
large block of memory and manage it ourselves via memory pools.

This change moves the cache entry allocation to be on top of memory
pools.

Design:

The index_state struct will gain a notion of an associated memory_pool
from which cache_entries will be allocated from. When reading in the
index from disk, we have information on the number of entries and
their size, which can guide us in deciding how large our initial
memory allocation should be. When an index is discarded, the
associated memory_pool will be discarded as well - so the lifetime of
a cache_entry is tied to the lifetime of the index_state that it was
allocated for.

In the case of a Split Index, the following rules are followed. 1st,
some terminology is defined:

Terminology:
  - 'the_index': represents the logical view of the index

  - 'split_index': represents the "base" cache entries. Read from the
    split index file.

'the_index' can reference a single split_index, as well as
cache_entries from the split_index. `the_index` will be discarded
before the `split_index` is.  This means that when we are allocating
cache_entries in the presence of a split index, we need to allocate
the entries from the `split_index`'s memory pool.  This allows us to
follow the pattern that `the_index` can reference cache_entries from
the `split_index`, and that the cache_entries will not be freed while
they are still being referenced.

Managing transient cache_entry structs:
Cache entries are usually allocated for an index, but this is not always
the case. Cache entries are sometimes allocated because this is the
type that the existing checkout_entry function works with. Because of
this, the existing code needs to handle cache entries associated with an
index / memory pool, and those that only exist transiently. Several
strategies were contemplated around how to handle this:

Chosen approach:
An extra field was added to the cache_entry type to track whether the
cache_entry was allocated from a memory pool or not. This is currently
an int field, as there are no more available bits in the existing
ce_flags bit field. If / when more bits are needed, this new field can
be turned into a proper bit field.

Alternatives:

1) Do not include any information about how the cache_entry was
allocated. Calling code would be responsible for tracking whether the
cache_entry needed to be freed or not.
  Pro: No extra memory overhead to track this state
  Con: Extra complexity in callers to handle this correctly.

The extra complexity and burden to not regress this behavior in the
future was more than we wanted.

2) cache_entry would gain knowledge about which mem_pool allocated it
  Pro: Could (potentially) do extra logic to know when a mem_pool no
       longer had references to any cache_entry
  Con: cache_entry would grow heavier by a pointer, instead of int

We didn't see a tangible benefit to this approach

3) Do not add any extra information to a cache_entry, but when freeing a
   cache entry, check if the memory exists in a region managed by existing
   mem_pools.
  Pro: No extra memory overhead to track state
  Con: Extra computation is performed when freeing cache entries

We decided tracking and iterating over known memory pool regions was
less desirable than adding an extra field to track this stae.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h        |  21 +++++++++
 mem-pool.c     |   3 +-
 read-cache.c   | 119 +++++++++++++++++++++++++++++++++++++++++--------
 split-index.c  |  50 +++++++++++++++++----
 unpack-trees.c |  13 +-----
 5 files changed, 167 insertions(+), 39 deletions(-)

diff --git a/cache.h b/cache.h
index 035a627bea..8fd89ae51f 100644
--- a/cache.h
+++ b/cache.h
@@ -15,6 +15,7 @@
 #include "path.h"
 #include "sha1-array.h"
 #include "repository.h"
+#include "mem-pool.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -156,6 +157,7 @@ struct cache_entry {
 	struct stat_data ce_stat_data;
 	unsigned int ce_mode;
 	unsigned int ce_flags;
+	unsigned int mem_pool_allocated;
 	unsigned int ce_namelen;
 	unsigned int index;	/* for link extension */
 	struct object_id oid;
@@ -227,6 +229,7 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 				    const struct cache_entry *src)
 {
 	unsigned int state = dst->ce_flags & CE_HASHED;
+	int mem_pool_allocated = dst->mem_pool_allocated;
 
 	/* Don't copy hash chain and name */
 	memcpy(&dst->ce_stat_data, &src->ce_stat_data,
@@ -235,6 +238,9 @@ static inline void copy_cache_entry(struct cache_entry *dst,
 
 	/* Restore the hash state */
 	dst->ce_flags = (dst->ce_flags & ~CE_HASHED) | state;
+
+	/* Restore the mem_pool_allocated flag */
+	dst->mem_pool_allocated = mem_pool_allocated;
 }
 
 static inline unsigned create_ce_flags(unsigned stage)
@@ -328,6 +334,7 @@ struct index_state {
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
+	struct mem_pool *ce_mem_pool;
 };
 
 extern struct index_state the_index;
@@ -373,6 +380,20 @@ struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Duplicate a cache_entry. Allocate memory for the new entry from a
+ * memory_pool. Takes into account cache_entry fields that are meant
+ * for managing the underlying memory allocation of the cache_entry.
+ */
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce, struct index_state *istate);
+
+/*
+ * Validate the cache entries in the index.  This is an internal
+ * consistency check that the cache_entry structs are allocated from
+ * the expected memory pool.
+ */
+void validate_cache_entries(const struct index_state *istate);
+
 #ifndef NO_THE_INDEX_COMPATIBILITY_MACROS
 #define active_cache (the_index.cache)
 #define active_nr (the_index.cache_nr)
diff --git a/mem-pool.c b/mem-pool.c
index b250a5fe40..139617cb23 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -54,7 +54,8 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 {
 	struct mp_block *block, *block_to_free;
 
-	while ((block = mem_pool->mp_block))
+	block = mem_pool->mp_block;
+	while (block)
 	{
 		block_to_free = block;
 		block = block->next_block;
diff --git a/read-cache.c b/read-cache.c
index 41e4d0e67a..b07369660b 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -46,6 +46,48 @@
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
 		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
+
+/*
+ * This is an estimate of the pathname length in the index.  We use
+ * this for V4 index files to guess the un-deltafied size of the index
+ * in memory because of pathname deltafication.  This is not required
+ * for V2/V3 index formats because their pathnames are not compressed.
+ * If the initial amount of memory set aside is not sufficient, the
+ * mem pool will allocate extra memory.
+ */
+#define CACHE_ENTRY_PATH_LENGTH 80
+
+static inline struct cache_entry *mem_pool__ce_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry *ce;
+	ce = mem_pool_alloc(mem_pool, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static inline struct cache_entry *mem_pool__ce_calloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct cache_entry * ce;
+	ce = mem_pool_calloc(mem_pool, 1, cache_entry_size(len));
+	ce->mem_pool_allocated = 1;
+	return ce;
+}
+
+static struct mem_pool *find_mem_pool(struct index_state *istate)
+{
+	struct mem_pool **pool_ptr;
+
+	if (istate->split_index && istate->split_index->base)
+		pool_ptr = &istate->split_index->base->ce_mem_pool;
+	else
+		pool_ptr = &istate->ce_mem_pool;
+
+	if (!*pool_ptr)
+		mem_pool_init(pool_ptr, 0);
+
+	return *pool_ptr;
+}
+
 struct index_state the_index;
 static const char *alternate_index_output;
 
@@ -746,7 +788,7 @@ int add_file_to_index(struct index_state *istate, const char *path, int flags)
 
 struct cache_entry *make_empty_cache_entry(struct index_state *istate, size_t len)
 {
-	return xcalloc(1, cache_entry_size(len));
+	return mem_pool__ce_calloc(find_mem_pool(istate), len);
 }
 
 struct cache_entry *make_empty_transient_cache_entry(size_t len)
@@ -1668,13 +1710,13 @@ int read_index(struct index_state *istate)
 	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
-static struct cache_entry *cache_entry_from_ondisk(struct index_state *istate,
+static struct cache_entry *cache_entry_from_ondisk(struct mem_pool *mem_pool,
 						   struct ondisk_cache_entry *ondisk,
 						   unsigned int flags,
 						   const char *name,
 						   size_t len)
 {
-	struct cache_entry *ce = make_empty_cache_entry(istate, len);
+	struct cache_entry *ce = mem_pool__ce_alloc(mem_pool, len);
 
 	ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
 	ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
@@ -1716,7 +1758,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
 	return (const char *)ep + 1 - cp_;
 }
 
-static struct cache_entry *create_from_disk(struct index_state *istate,
+static struct cache_entry *create_from_disk(struct mem_pool *mem_pool,
 					    struct ondisk_cache_entry *ondisk,
 					    unsigned long *ent_size,
 					    struct strbuf *previous_name)
@@ -1748,13 +1790,13 @@ static struct cache_entry *create_from_disk(struct index_state *istate,
 		/* v3 and earlier */
 		if (len == CE_NAMEMASK)
 			len = strlen(name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags, name, len);
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags, name, len);
 
 		*ent_size = ondisk_ce_size(ce);
 	} else {
 		unsigned long consumed;
 		consumed = expand_name_field(previous_name, name);
-		ce = cache_entry_from_ondisk(istate, ondisk, flags,
+		ce = cache_entry_from_ondisk(mem_pool, ondisk, flags,
 					     previous_name->buf,
 					     previous_name->len);
 
@@ -1828,6 +1870,22 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_fsmonitor(istate);
 }
 
+static size_t estimate_cache_size_from_compressed(unsigned int entries)
+{
+	return entries * (sizeof(struct cache_entry) + CACHE_ENTRY_PATH_LENGTH);
+}
+
+static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
+{
+	long per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
+
+	/*
+	 * Account for potential alignment differences.
+	 */
+	per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry));
+	return ondisk_size + entries * per_entry;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1874,10 +1932,15 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(*istate->cache));
 	istate->initialized = 1;
 
-	if (istate->version == 4)
+	if (istate->version == 4) {
 		previous_name = &previous_name_buf;
-	else
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size_from_compressed(istate->cache_nr));
+	} else {
 		previous_name = NULL;
+		mem_pool_init(&istate->ce_mem_pool,
+			      estimate_cache_size(mmap_size, istate->cache_nr));
+	}
 
 	src_offset = sizeof(*hdr);
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -1886,7 +1949,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		unsigned long consumed;
 
 		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-		ce = create_from_disk(istate, disk_ce, &consumed, previous_name);
+		ce = create_from_disk(istate->ce_mem_pool, disk_ce, &consumed, previous_name);
 		set_index_entry(istate, i, ce);
 
 		src_offset += consumed;
@@ -1983,17 +2046,13 @@ int is_index_unborn(struct index_state *istate)
 
 int discard_index(struct index_state *istate)
 {
-	int i;
+	/*
+	 * Cache entries in istate->cache[] should have been allocated
+	 * from the memory pool associated with this index, or from an
+	 * associated split_index. There is no need to free individual
+	 * cache entries.
+	 */
 
-	for (i = 0; i < istate->cache_nr; i++) {
-		if (istate->cache[i]->index &&
-		    istate->split_index &&
-		    istate->split_index->base &&
-		    istate->cache[i]->index <= istate->split_index->base->cache_nr &&
-		    istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
-			continue;
-		discard_cache_entry(istate->cache[i]);
-	}
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
 	istate->cache_changed = 0;
@@ -2007,6 +2066,12 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+
+	if (istate->ce_mem_pool) {
+		mem_pool_discard(istate->ce_mem_pool);
+		istate->ce_mem_pool = NULL;
+	}
+
 	return 0;
 }
 
@@ -2798,7 +2863,23 @@ void move_index_extensions(struct index_state *dst, struct index_state *src)
 	src->untracked = NULL;
 }
 
+struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
+				    struct index_state *istate)
+{
+	unsigned int size = ce_size(ce);
+	int mem_pool_allocated;
+	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
+	mem_pool_allocated = new_entry->mem_pool_allocated;
+
+	memcpy(new_entry, ce, size);
+	new_entry->mem_pool_allocated = mem_pool_allocated;
+	return new_entry;
+}
+
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && ce->mem_pool_allocated)
+		return;
+
 	free(ce);
 }
diff --git a/split-index.c b/split-index.c
index 317900db8b..84f067e10d 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,16 +73,31 @@ void move_cache_to_base_index(struct index_state *istate)
 	int i;
 
 	/*
-	 * do not delete old si->base, its index entries may be shared
-	 * with istate->cache[]. Accept a bit of leaking here because
-	 * this code is only used by short-lived update-index.
+	 * If there was a previous base index, then transfer ownership of allocated
+	 * entries to the parent index.
 	 */
+	if (si->base &&
+		si->base->ce_mem_pool) {
+
+		if (!istate->ce_mem_pool)
+			mem_pool_init(&istate->ce_mem_pool, 0);
+
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+	}
+
 	si->base = xcalloc(1, sizeof(*si->base));
 	si->base->version = istate->version;
 	/* zero timestamp disables racy test in ce_write_index() */
 	si->base->timestamp = istate->timestamp;
 	ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
 	si->base->cache_nr = istate->cache_nr;
+
+	/*
+	 * The mem_pool needs to move with the allocated entries.
+	 */
+	si->base->ce_mem_pool = istate->ce_mem_pool;
+	istate->ce_mem_pool = NULL;
+
 	COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
 	mark_base_index_entries(si->base);
 	for (i = 0; i < si->base->cache_nr; i++)
@@ -331,12 +346,31 @@ void remove_split_index(struct index_state *istate)
 {
 	if (istate->split_index) {
 		/*
-		 * can't discard_split_index(&the_index); because that
-		 * will destroy split_index->base->cache[], which may
-		 * be shared with the_index.cache[]. So yeah we're
-		 * leaking a bit here.
+		 * When removing the split index, we need to move
+		 * ownership of the mem_pool associated with the
+		 * base index to the main index. There may be cache entries
+		 * allocated from the base's memory pool that are shared with
+		 * the_index.cache[].
 		 */
-		istate->split_index = NULL;
+		mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
+
+		/*
+		 * The split index no longer owns the mem_pool backing
+		 * its cache array. As we are discarding this index,
+		 * mark the index as having no cache entries, so it
+		 * will not attempt to clean up the cache entries or
+		 * validate them.
+		 */
+		if (istate->split_index->base)
+			istate->split_index->base->cache_nr = 0;
+
+		/*
+		 * We can discard the split index because its
+		 * memory pool has been incorporated into the
+		 * memory pool associated with the the_index.
+		 */
+		discard_split_index(istate);
+
 		istate->cache_changed |= SOMETHING_CHANGED;
 	}
 }
diff --git a/unpack-trees.c b/unpack-trees.c
index 33cba550b0..a3b5131732 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -203,20 +203,11 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
-static struct cache_entry *dup_entry(const struct cache_entry *ce, struct index_state *istate)
-{
-	unsigned int size = ce_size(ce);
-	struct cache_entry *new_entry = make_empty_cache_entry(istate, ce_namelen(ce));
-
-	memcpy(new_entry, ce, size);
-	return new_entry;
-}
-
 static void add_entry(struct unpack_trees_options *o,
 		      const struct cache_entry *ce,
 		      unsigned int set, unsigned int clear)
 {
-	do_add_entry(o, dup_entry(ce, &o->result), set, clear);
+	do_add_entry(o, dup_cache_entry(ce, &o->result), set, clear);
 }
 
 /*
@@ -1802,7 +1793,7 @@ static int merged_entry(const struct cache_entry *ce,
 			struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
-	struct cache_entry *merge = dup_entry(ce, &o->result);
+	struct cache_entry *merge = dup_cache_entry(ce, &o->result);
 
 	if (!old) {
 		/*
-- 
2.17.1

[PATCH v6 8/8] block alloc: add validations around cache_entry lifecyle

[Jameson Miller]

Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:

  1) Invalidate cache_entry memory when discarding cache_entry.

  2) When discarding index_state struct, verify that all cache_entries
     were allocated from expected mem_pool.

  3) When discarding mem_pools, invalidate mem_pool memory.

This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.

Signed-off-by: Jameson Miller <jamill@microsoft.com>
---
 cache.h      |  6 ++++++
 git.c        |  3 +++
 mem-pool.c   |  6 +++++-
 mem-pool.h   |  2 +-
 read-cache.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 5 files changed, 68 insertions(+), 4 deletions(-)

diff --git a/cache.h b/cache.h
index 8fd89ae51f..b3faef3efc 100644
--- a/cache.h
+++ b/cache.h
@@ -380,6 +380,12 @@ struct cache_entry *make_empty_transient_cache_entry(size_t name_len);
  */
 void discard_cache_entry(struct cache_entry *ce);
 
+/*
+ * Check configuration if we should perform extra validation on cache
+ * entries.
+ */
+int should_validate_cache_entries(void);
+
 /*
  * Duplicate a cache_entry. Allocate memory for the new entry from a
  * memory_pool. Takes into account cache_entry fields that are meant
diff --git a/git.c b/git.c
index 9dbe6ffaa7..c7e4f0351a 100644
--- a/git.c
+++ b/git.c
@@ -414,7 +414,10 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 
 	trace_argv_printf(argv, "trace: built-in: git");
 
+	validate_cache_entries(&the_index);
 	status = p->fn(argc, argv, prefix);
+	validate_cache_entries(&the_index);
+
 	if (status)
 		return status;
 
diff --git a/mem-pool.c b/mem-pool.c
index 139617cb23..a2841a4a9a 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -50,7 +50,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
 	*mem_pool = pool;
 }
 
-void mem_pool_discard(struct mem_pool *mem_pool)
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory)
 {
 	struct mp_block *block, *block_to_free;
 
@@ -59,6 +59,10 @@ void mem_pool_discard(struct mem_pool *mem_pool)
 	{
 		block_to_free = block;
 		block = block->next_block;
+
+		if (invalidate_memory)
+			memset(block_to_free->space, 0xDD, ((char *)block_to_free->end) - ((char *)block_to_free->space));
+
 		free(block_to_free);
 	}
 
diff --git a/mem-pool.h b/mem-pool.h
index adeefdcb28..999d3c3a52 100644
--- a/mem-pool.h
+++ b/mem-pool.h
@@ -29,7 +29,7 @@ void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size);
 /*
  * Discard a memory pool and free all the memory it is responsible for.
  */
-void mem_pool_discard(struct mem_pool *mem_pool);
+void mem_pool_discard(struct mem_pool *mem_pool, int invalidate_memory);
 
 /*
  * Alloc memory from the mem_pool.
diff --git a/read-cache.c b/read-cache.c
index b07369660b..fd67e2e8a4 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2050,8 +2050,10 @@ int discard_index(struct index_state *istate)
 	 * Cache entries in istate->cache[] should have been allocated
 	 * from the memory pool associated with this index, or from an
 	 * associated split_index. There is no need to free individual
-	 * cache entries.
+	 * cache entries. validate_cache_entries can detect when this
+	 * assertion does not hold.
 	 */
+	validate_cache_entries(istate);
 
 	resolve_undo_clear_index(istate);
 	istate->cache_nr = 0;
@@ -2068,13 +2070,45 @@ int discard_index(struct index_state *istate)
 	istate->untracked = NULL;
 
 	if (istate->ce_mem_pool) {
-		mem_pool_discard(istate->ce_mem_pool);
+		mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
 		istate->ce_mem_pool = NULL;
 	}
 
 	return 0;
 }
 
+/*
+ * Validate the cache entries of this index.
+ * All cache entries associated with this index
+ * should have been allocated by the memory pool
+ * associated with this index, or by a referenced
+ * split index.
+ */
+void validate_cache_entries(const struct index_state *istate)
+{
+	int i;
+
+	if (!should_validate_cache_entries() ||!istate || !istate->initialized)
+		return;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (!istate) {
+			die("internal error: cache entry is not allocated from expected memory pool");
+		} else if (!istate->ce_mem_pool ||
+			!mem_pool_contains(istate->ce_mem_pool, istate->cache[i])) {
+			if (!istate->split_index ||
+				!istate->split_index->base ||
+				!istate->split_index->base->ce_mem_pool ||
+				!mem_pool_contains(istate->split_index->base->ce_mem_pool, istate->cache[i])) {
+				die("internal error: cache entry is not allocated from expected memory pool");
+			}
+		}
+	}
+
+	if (istate->split_index)
+		validate_cache_entries(istate->split_index->base);
+}
+
 int unmerged_index(const struct index_state *istate)
 {
 	int i;
@@ -2878,8 +2912,25 @@ struct cache_entry *dup_cache_entry(const struct cache_entry *ce,
 
 void discard_cache_entry(struct cache_entry *ce)
 {
+	if (ce && should_validate_cache_entries())
+		memset(ce, 0xCD, cache_entry_size(ce->ce_namelen));
+
 	if (ce && ce->mem_pool_allocated)
 		return;
 
 	free(ce);
 }
+
+int should_validate_cache_entries(void)
+{
+	static int validate_index_cache_entries = -1;
+
+	if (validate_index_cache_entries < 0) {
+		if (getenv("GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES"))
+			validate_index_cache_entries = 1;
+		else
+			validate_index_cache_entries = 0;
+	}
+
+	return validate_index_cache_entries;
+}
-- 
2.17.1