From: Abhishek Kumar <abhishekkumar8222@gmail.com>
To: git@vger.kernel.org
Cc: jnareb@gmail.com, stolee@gmail.com
Subject: [GSOC Patch v4 2/4] commit-graph: introduce commit_graph_data_slab
Date: Wed, 17 Jun 2020 14:44:09 +0530 [thread overview]
Message-ID: <20200617091411.14650-3-abhishekkumar8222@gmail.com> (raw)
In-Reply-To: <20200617091411.14650-1-abhishekkumar8222@gmail.com>
The struct commit is used in many contexts. However, members
`generation` and `graph_pos` are only used for commit-graph related
operations and otherwise waste memory.
This wastage would have been more pronounced as we transition to
generation number v2, which uses 64-bit generation number instead of
current 32-bits.
As they are often accessed together, let's introduce struct
commit_graph_data and move them to a commit_graph_data slab.
While the overall test suite runs just as fast as master,
(series: 26m48s, master: 27m34s, faster by 2.87%), certain commands
like `git merge-base --is-ancestor` were slowed by 40% as discovered
by Szeder Gábor [1]. After minimizing commit-slab access, the slow down
persists but is closer to 20%.
Derrick Stolee believes the slow down is attributable to the underlying
algorithm rather than the slowness of commit-slab access [2] and we will
follow-up in a later series.
[1]: https://lore.kernel.org/git/20200607195347.GA8232@szeder.dev/
[2]: https://lore.kernel.org/git/13db757a-9412-7f1e-805c-8a028c4ab2b1@gmail.com/
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
---
On linux.git with HEAD at 08bf1a27 (Merge tag 'powerpc-5.8-2' of
git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux,
2020-06-13):
`git merge-base --is-ancestor HEAD~50000 HEAD`
Time (master): 0.787s
Time (series): 0.927s
Change: 17.79% (slower)
Max RSS (master): 177694kb
Max RSS (series): 177707kb
Change: 0.01% (more)
`git gc`
Time (master): 3m55s
Time (series): 3m38s
Change: 7.23% (faster)
Max RSS (master): 4889868kb
Max RSS (series): 4911960kb
Change: 0.45% (more)
Earlier implementation of commit_graph_data_at() was incorrect, as we
used to iterate from old slab count to new slab count - assuming all
intermediate slabs are allocated. This is incorrect as the slabs are
allocated only when there's a corresponding commit.
It now makes *two slab accesses* in the worst case, but it's okay since
the worst case occurs once nearly every (512kb / 8b) commits.
commit-graph.c | 78 +++++++++++++++++++++++++++++++++++++++++++-------
commit-graph.h | 10 +++++++
2 files changed, 78 insertions(+), 10 deletions(-)
diff --git a/commit-graph.c b/commit-graph.c
index 2ff042fbf4..8ad7d202b2 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -87,6 +87,58 @@ static int commit_pos_cmp(const void *va, const void *vb)
commit_pos_at(&commit_pos, b);
}
+define_commit_slab(commit_graph_data_slab, struct commit_graph_data);
+static struct commit_graph_data_slab commit_graph_data_slab =
+ COMMIT_SLAB_INIT(1, commit_graph_data_slab);
+
+uint32_t commit_graph_position(const struct commit *c)
+{
+ struct commit_graph_data *data =
+ commit_graph_data_slab_peek(&commit_graph_data_slab, c);
+
+ return data ? data->graph_pos : COMMIT_NOT_FROM_GRAPH;
+}
+
+uint32_t commit_graph_generation(const struct commit *c)
+{
+ struct commit_graph_data *data =
+ commit_graph_data_slab_peek(&commit_graph_data_slab, c);
+
+ if (!data)
+ return GENERATION_NUMBER_INFINITY;
+ else if (data->graph_pos == COMMIT_NOT_FROM_GRAPH)
+ return GENERATION_NUMBER_INFINITY;
+
+ return data->generation;
+}
+
+static struct commit_graph_data *commit_graph_data_at(const struct commit *c)
+{
+ unsigned int i, nth_slab;
+ struct commit_graph_data *data =
+ commit_graph_data_slab_peek(&commit_graph_data_slab, c);
+
+ if (data)
+ return data;
+
+ nth_slab = c->index / commit_graph_data_slab.slab_size;
+ data = commit_graph_data_slab_at(&commit_graph_data_slab, c);
+
+ /*
+ * commit-slab initializes elements with zero, overwrite this with
+ * COMMIT_NOT_FROM_GRAPH for graph_pos.
+ *
+ * We avoid initializing generation with checking if graph position
+ * is not COMMIT_NOT_FROM_GRAPH.
+ */
+ for (i = 0; i < commit_graph_data_slab.slab_size; i++) {
+ commit_graph_data_slab.slab[nth_slab][i].graph_pos =
+ COMMIT_NOT_FROM_GRAPH;
+ }
+
+ return data;
+}
+
static int commit_gen_cmp(const void *va, const void *vb)
{
const struct commit *a = *(const struct commit **)va;
@@ -1020,7 +1072,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
else
packedDate[0] = 0;
- packedDate[0] |= htonl((*list)->generation << 2);
+ packedDate[0] |= htonl(commit_graph_data_at(*list)->generation << 2);
packedDate[1] = htonl((*list)->date);
hashwrite(f, packedDate, 8);
@@ -1251,9 +1303,11 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
_("Computing commit graph generation numbers"),
ctx->commits.nr);
for (i = 0; i < ctx->commits.nr; i++) {
+ uint32_t generation = commit_graph_data_at(ctx->commits.list[i])->generation;
+
display_progress(ctx->progress, i + 1);
- if (ctx->commits.list[i]->generation != GENERATION_NUMBER_INFINITY &&
- ctx->commits.list[i]->generation != GENERATION_NUMBER_ZERO)
+ if (generation != GENERATION_NUMBER_INFINITY &&
+ generation != GENERATION_NUMBER_ZERO)
continue;
commit_list_insert(ctx->commits.list[i], &list);
@@ -1264,22 +1318,26 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
uint32_t max_generation = 0;
for (parent = current->parents; parent; parent = parent->next) {
- if (parent->item->generation == GENERATION_NUMBER_INFINITY ||
- parent->item->generation == GENERATION_NUMBER_ZERO) {
+ generation = commit_graph_data_at(parent->item)->generation;
+
+ if (generation == GENERATION_NUMBER_INFINITY ||
+ generation == GENERATION_NUMBER_ZERO) {
all_parents_computed = 0;
commit_list_insert(parent->item, &list);
break;
- } else if (parent->item->generation > max_generation) {
- max_generation = parent->item->generation;
+ } else if (generation > max_generation) {
+ max_generation = generation;
}
}
if (all_parents_computed) {
- current->generation = max_generation + 1;
+ struct commit_graph_data *data = commit_graph_data_at(current);
+
+ data->generation = max_generation + 1;
pop_commit(&list);
- if (current->generation > GENERATION_NUMBER_MAX)
- current->generation = GENERATION_NUMBER_MAX;
+ if (data->generation > GENERATION_NUMBER_MAX)
+ data->generation = GENERATION_NUMBER_MAX;
}
}
}
diff --git a/commit-graph.h b/commit-graph.h
index 3ba0da1e5f..28f89cdf3e 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -135,4 +135,14 @@ void free_commit_graph(struct commit_graph *);
*/
void disable_commit_graph(struct repository *r);
+struct commit_graph_data {
+ uint32_t graph_pos;
+ uint32_t generation;
+};
+
+/*
+ * Commits should be parsed before accessing generation, graph positions.
+ */
+uint32_t commit_graph_generation(const struct commit *);
+uint32_t commit_graph_position(const struct commit *);
#endif
--
2.27.0
next prev parent reply other threads:[~2020-06-17 9:16 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 7:27 [GSoC Patch 0/3] Move generation, graph_pos to a slab Abhishek Kumar
2020-06-04 7:27 ` [GSoC Patch 1/3] commit: introduce helpers for generation slab Abhishek Kumar
2020-06-04 14:36 ` Derrick Stolee
2020-06-04 17:35 ` Junio C Hamano
2020-06-05 23:23 ` Jakub Narębski
2020-06-04 7:27 ` [GSoC Patch 2/3] commit: convert commit->generation to a slab Abhishek Kumar
2020-06-04 14:27 ` Derrick Stolee
2020-06-04 17:49 ` Junio C Hamano
2020-06-06 22:03 ` Jakub Narębski
2020-06-04 7:27 ` [GSoC Patch 3/3] commit: convert commit->graph_pos " Abhishek Kumar
2020-06-07 12:12 ` Jakub Narębski
2020-06-04 14:22 ` [GSoC Patch 0/3] Move generation, graph_pos " Derrick Stolee
2020-06-04 17:55 ` Junio C Hamano
2020-06-07 19:53 ` SZEDER Gábor
2020-06-08 5:48 ` Abhishek Kumar
2020-06-08 8:36 ` SZEDER Gábor
2020-06-08 13:45 ` Derrick Stolee
2020-06-08 16:46 ` SZEDER Gábor
2020-06-08 15:21 ` Jakub Narębski
2020-06-05 19:00 ` Jakub Narębski
2020-06-07 19:32 ` [GSOC Patch v2 0/4] " Abhishek Kumar
2020-06-07 19:32 ` [GSOC Patch v2 1/4] commit-graph: introduce commit_graph_data_slab Abhishek Kumar
2020-06-15 16:27 ` Taylor Blau
2020-06-07 19:32 ` [GSOC Patch v2 2/4] commit: move members graph_pos, generation to a slab Abhishek Kumar
2020-06-08 8:26 ` SZEDER Gábor
2020-06-08 12:35 ` Derrick Stolee
2020-06-07 19:32 ` [GSOC Patch v2 3/4] commit-graph: use generation directly when writing commit-graph Abhishek Kumar
2020-06-08 16:31 ` Jakub Narębski
2020-06-15 16:31 ` Taylor Blau
2020-06-07 19:32 ` [GSOC Patch v2 4/4] commit-graph: minimize commit_graph_data_slab access Abhishek Kumar
2020-06-08 16:22 ` [GSOC Patch v2 0/4] Move generation, graph_pos to a slab Jakub Narębski
2020-06-15 16:24 ` Taylor Blau
2020-06-17 9:14 ` [GSOC Patch v4 " Abhishek Kumar
2020-06-17 9:14 ` [GSOC Patch v4 1/4] object: drop parsed_object_pool->commit_count Abhishek Kumar
2020-06-17 9:14 ` Abhishek Kumar [this message]
2020-06-17 9:14 ` [GSOC Patch v4 3/4] commit: move members graph_pos, generation to a slab Abhishek Kumar
2020-06-17 9:14 ` [GSOC Patch v4 4/4] commit-graph: minimize commit_graph_data_slab access Abhishek Kumar
2020-06-19 13:59 ` [GSOC Patch v4 0/4] Move generation, graph_pos to a slab Derrick Stolee
2020-06-19 17:44 ` Junio C Hamano
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