Re: Corrupt name-rev output

["René Scharfe" <l.s.r@web.de>]

Am 21.04.22 um 19:55 schrieb René Scharfe:
> Am 21.04.22 um 04:11 schrieb Elijah Newren:
>
>> Reverting 2d53975488 fixes the problem.
>
> That's a good band-aid.
Or perhaps it's all we need.  I can't replicate the original reduction
of peak memory usage for the Chromium repo anymore.  In fact, the very
next commit, 079f970971 (name-rev: sort tip names before applying,
2020-02-05), reduced the number of times free(3) is called there from
44245 to 5, and 3656f84278 (name-rev: prefer shorter names over
following merges, 2021-12-04) brought that number down to zero.

I can't reproduce the issue with the hardenedBSD repo, by the way, but
e.g. with 'git name-rev 58b82150da' in the Linux repo.

--- >8 ---
Subject: [PATCH] Revert "name-rev: release unused name strings"

This reverts commit 2d53975488df195e1431c3f90bfb5b60018d5bf6.

3656f84278 (name-rev: prefer shorter names over following merges,
2021-12-04) broke the assumption of 2d53975488 (name-rev: release unused
name strings, 2020-02-04) that a better name for a child is a better
name for all of its ancestors as well, because it added a penalty for
generation > 0.  This leads to strings being free(3)'d that are still
needed.

079f970971 (name-rev: sort tip names before applying, 2020-02-05)
already reduced the number of free(3) calls for the use case that
motivated the original patch (name-rev --all in the Chromium repository)
from ca. 44000 to 5, and 3656f84278 eliminated even those few.  So this
revert won't affect name-rev's performance on that particular repo.

Reported-by: Thomas Hurst <tom@hur.st>
Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
---
 builtin/name-rev.c | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index c59b5699fe..02ea9d1633 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -18,7 +18,7 @@
 #define CUTOFF_DATE_SLOP 86400

 struct rev_name {
-	char *tip_name;
+	const char *tip_name;
 	timestamp_t taggerdate;
 	int generation;
 	int distance;
@@ -84,7 +84,7 @@ static int commit_is_before_cutoff(struct commit *commit)

 static int is_valid_rev_name(const struct rev_name *name)
 {
-	return name && (name->generation || name->tip_name);
+	return name && name->tip_name;
 }

 static struct rev_name *get_commit_rev_name(const struct commit *commit)
@@ -146,20 +146,9 @@ static struct rev_name *create_or_update_name(struct commit *commit,
 {
 	struct rev_name *name = commit_rev_name_at(&rev_names, commit);

-	if (is_valid_rev_name(name)) {
-		if (!is_better_name(name, taggerdate, generation, distance, from_tag))
-			return NULL;
-
-		/*
-		 * This string might still be shared with ancestors
-		 * (generation > 0).  We can release it here regardless,
-		 * because the new name that has just won will be better
-		 * for them as well, so name_rev() will replace these
-		 * stale pointers when it processes the parents.
-		 */
-		if (!name->generation)
-			free(name->tip_name);
-	}
+	if (is_valid_rev_name(name) &&
+	    !is_better_name(name, taggerdate, generation, distance, from_tag))
+		return NULL;

 	name->taggerdate = taggerdate;
 	name->generation = generation;
--
2.35.3