@@ -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;
}
}
}
@@ -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
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(-)