On Mon, Sep 23, 2019 at 09:55:11PM +0200, René Scharfe wrote:
> -- >8 --
> Subject: [PATCH] name-rev: use FLEX_ARRAY for tip_name in struct rev_name
>
> Give each rev_name its very own tip_name string. This simplifies memory
> ownership, as callers of name_rev() only have to make sure the tip_name
> parameter exists for the duration of the call and don't have to preserve
> it for the whole run of the program.
>
> It also saves four or eight bytes per object because this change removes
> the pointer indirection. Memory usage is still higher for linear
> histories that previously shared the same tip_name value between
> multiple name_rev instances.
Besides looking at memory usage, have you run any performance
benchmarks? Here it seems to make 'git name-rev --all >out' slower by
17% in the git repo and by 19.5% in the linux repo.
> Signed-off-by: René Scharfe <l.s.r@xxxxxx>
> ---
> builtin/name-rev.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/builtin/name-rev.c b/builtin/name-rev.c
> index c785fe16ba..4162fb29ee 100644
> --- a/builtin/name-rev.c
> +++ b/builtin/name-rev.c
> @@ -12,11 +12,11 @@
> #define CUTOFF_DATE_SLOP 86400 /* one day */
>
> typedef struct rev_name {
> - const char *tip_name;
> timestamp_t taggerdate;
> int generation;
> int distance;
> int from_tag;
> + char tip_name[FLEX_ARRAY];
> } rev_name;
>
> define_commit_slab(commit_rev_name, struct rev_name *);
> @@ -97,17 +97,14 @@ static void name_rev(struct commit *commit,
> die("generation: %d, but deref?", generation);
> }
>
> - if (name == NULL) {
> - name = xmalloc(sizeof(rev_name));
> - set_commit_rev_name(commit, name);
> - goto copy_data;
> - } else if (is_better_name(name, taggerdate, distance, from_tag)) {
> -copy_data:
> - name->tip_name = tip_name;
> + if (!name || is_better_name(name, taggerdate, distance, from_tag)) {
> + free(name);
> + FLEX_ALLOC_STR(name, tip_name, tip_name);
> name->taggerdate = taggerdate;
> name->generation = generation;
> name->distance = distance;
> name->from_tag = from_tag;
> + set_commit_rev_name(commit, name);
> } else {
> free(to_free);
> return;
> @@ -131,12 +128,14 @@ static void name_rev(struct commit *commit,
> name_rev(parents->item, new_name, taggerdate, 0,
> distance + MERGE_TRAVERSAL_WEIGHT,
> from_tag, 0);
> + free(new_name);
> } else {
> name_rev(parents->item, tip_name, taggerdate,
> generation + 1, distance + 1,
> from_tag, 0);
> }
> }
> + free(to_free);
> }
>
> static int subpath_matches(const char *path, const char *filter)
> @@ -270,8 +269,7 @@ static int name_ref(const char *path, const struct object_id *oid, int flags, vo
> if (taggerdate == TIME_MAX)
> taggerdate = ((struct commit *)o)->date;
> path = name_ref_abbrev(path, can_abbreviate_output);
> - name_rev(commit, xstrdup(path), taggerdate, 0, 0,
> - from_tag, deref);
> + name_rev(commit, path, taggerdate, 0, 0, from_tag, deref);
> }
> return 0;
> }
> --
> 2.23.0
