From: Karthik Nayak Date: Wed, 10 Jun 2026 11:47:17 GMT Subject: Re: [PATCH v2 2/2] ref-filter: memoize --contains with generations Message-ID: In-Reply-To: <20260608-ref-filter-memoized-contains-v2-2-e72720344a7c@gmail.com> Tamir Duberstein writes: > git branch and git for-each-ref call repo_is_descendant_of() for > each candidate selected by --contains or --no-contains. Each call > starts a new graph walk, so refs with shared history repeatedly > traverse the same commits. > > ffc4b8012d (tag: speed up --contains calculation, 2011-06-11) > introduced a depth-first walk for git tag that caches positive and > negative answers across candidates. ee2bd06b0f (ref-filter: implement > '--contains' option, 2015-07-07) preserved both implementations when > ref-filter learned --contains. > > The memoized walk is not always faster. Without generation numbers, > a negative check can walk to the root even when the breadth-first > merge-base walk finds a nearby divergence. With generation numbers, > the depth-first walk can stop below the oldest target while still > reusing answers across candidates. > > Keep the existing memoized selection for git tag. Select it for other > ref-filter callers when generation numbers are enabled, and retain > the breadth-first walk otherwise. > > When generation numbers are unavailable, repo_is_descendant_of() can > return -1 if ancestry cannot be read. The ref-filter Boolean interface > treated that error as a match. Check it and exit instead. The memoized > path already dies on the same parse failure, so both selected paths now > fail rather than return a result. > > Add p1500 cases for up to 8,192 packed refs along one first-parent > history and for sibling refs near the tip with generation numbers > forced off. > > On a checkout with 62,174 remote-tracking refs and generation numbers > enabled, I ran: > > hyperfine --warmup 0 --runs 3 \ > --command-name parent \ > '"$parent" branch -r --contains c78ae85f3ce7e >/dev/null' \ > --command-name this-commit \ > '"$this" branch -r --contains c78ae85f3ce7e >/dev/null' > > The results were: > > parent this commit > elapsed 104.365 s 467.7 ms > user 93.702 s 220.2 ms > system 0.723 s 182.7 ms > > The wall-time standard deviations were 11.356 seconds and 133.8 > milliseconds, respectively. Separate runs without redirection produced > the same output with SHA-256 > 2466f6e2b72aa16b1a2126eddb81c8a1b2764ee251204ac034c191a925aa896f. > > Both revisions were built with the default -O2 flags using Apple > clang 21.0.0 on macOS 26.5. The machine was a MacBook Pro (Mac16,6) > with a 16-core Apple M4 Max (12 performance and four efficiency > cores) and 128 GB RAM. > > Link: https://lore.kernel.org/git/1445163904-24611-1-git-send-email-Karthik.188@gmail.com/ > Link: https://lore.kernel.org/r/20230324191009.GA536967@coredump.intra.peff.net > Link: https://lore.kernel.org/git/20260527070510.3510836-1-krka@spotify.com/ > Link: https://lore.kernel.org/r/20260608223430.GA340696@coredump.intra.peff.net > Suggested-by: Jeff King > Signed-off-by: Tamir Duberstein > --- > commit-reach.c | 13 +++++++++-- > commit-reach.h | 7 ++++++ > t/perf/p1500-graph-walks.sh | 49 +++++++++++++++++++++++++++++++++++++++++- > t/t6301-for-each-ref-errors.sh | 22 +++++++++++++++++++ > 4 files changed, 88 insertions(+), 3 deletions(-) > > diff --git a/commit-reach.c b/commit-reach.c > index 65b618959b..83a48004ef 100644 > --- a/commit-reach.c > +++ b/commit-reach.c > @@ -821,9 +821,18 @@ static enum contains_result contains_tag_algo(struct commit *candidate, > int commit_contains(struct ref_filter *filter, struct commit *commit, > struct commit_list *list, struct contains_cache *cache) > { > - if (filter->with_commit_tag_algo) > + int result; > + > + if (!list) > + return 1; > + if (filter->with_commit_tag_algo || > + generation_numbers_enabled(the_repository)) What's stopping us from dropping `filter->with_commit_tag_algo` completely and then doing? if (generation_numbers_enabled(the_repository)) return contains_algo(commit, list, cache) == CONTAINS_YES; return repo_is_descendant_of(the_repository, commit, list); [snip]