Re: [PATCH v2 07/15] rev-list: allow bitmaps when counting objects

[Taylor Blau <me@ttaylorr.com>]

On Fri, Feb 14, 2020 at 01:22:22PM -0500, Jeff King wrote:
> The prior commit taught "--count --objects" to work without bitmaps. We
> should be able to get the same answer much more quickly with bitmaps.
>
> Note that we punt on the max_count case here. This perhaps _could_ be
> made to work if we find all of the boundary commits and treat them as
> UNINTERESTING, subtracting them (and their reachable objects) from the
> set we return. That implies an actual commit traversal, but we'd still
> be faster due to avoiding opening up any trees. Given the complexity and
> the fact that anyone is unlikely to want this, it makes sense to just
> fall back to the non-bitmap case for now.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  builtin/rev-list.c      | 21 ++++++++++++++++++---
>  t/t5310-pack-bitmaps.sh |  6 ++++++
>  2 files changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/rev-list.c b/builtin/rev-list.c
> index 9452123988..70f3207ecc 100644
> --- a/builtin/rev-list.c
> +++ b/builtin/rev-list.c
> @@ -374,7 +374,10 @@ static inline int parse_missing_action_value(const char *value)
>
>  static int try_bitmap_count(struct rev_info *revs)
>  {
> -	uint32_t commit_count;
> +	uint32_t commit_count = 0,
> +		 tag_count = 0,
> +		 tree_count = 0,
> +		 blob_count = 0;

Hmm, I don't usually see the comma-separated declaration/initialization
in git.git. Is there a reason you did it here? Not that I really mind
one way or the other, just interested.

>  	int max_count;
>  	struct bitmap_index *bitmap_git;
>
> @@ -389,6 +392,15 @@ static int try_bitmap_count(struct rev_info *revs)
>  	if (revs->left_right || revs->cherry_mark)
>  		return -1;
>
> +	/*
> +	 * If we're counting reachable objects, we can't handle a max count of
> +	 * commits to traverse, since we don't know which objects go with which
> +	 * commit.
> +	 */
> +	if (revs->max_count >= 0 &&
> +	    (revs->tag_objects || revs->tree_objects || revs->blob_objects))

An aside unrelated to the patch at hand: the expression

  (revs->tag_objects || revs->tree_objects || revs->blob_objects)

does occur in an awful lot of places throughout this file. Do you
imagine it'd be useful to pull this check out into its own function,
perhaps as a preparatory patch in a later version of this series?

I'm also not fussed if you don't think that such a change would be
useful, it's just an observation I had after seeing this expression a
few times.

> +		return -1;
> +
>  	/*
>  	 * This must be saved before doing any walking, since the revision
>  	 * machinery will count it down to zero while traversing.
> @@ -399,11 +411,14 @@ static int try_bitmap_count(struct rev_info *revs)
>  	if (!bitmap_git)
>  		return -1;
>
> -	count_bitmap_commit_list(bitmap_git, &commit_count, NULL, NULL, NULL);
> +	count_bitmap_commit_list(bitmap_git, &commit_count,
> +				 revs->tree_objects ? &tree_count : NULL,
> +				 revs->blob_objects ? &blob_count : NULL,
> +				 revs->tag_objects ? &tag_count : NULL);
>  	if (max_count >= 0 && max_count < commit_count)
>  		commit_count = max_count;
>
> -	printf("%d\n", commit_count);
> +	printf("%d\n", commit_count + tree_count + blob_count + tag_count);
>  	free_bitmap_index(bitmap_git);
>  	return 0;
>  }
> diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
> index 6640329ebf..7ba7d294a5 100755
> --- a/t/t5310-pack-bitmaps.sh
> +++ b/t/t5310-pack-bitmaps.sh
> @@ -74,6 +74,12 @@ rev_list_tests() {
>  		test_cmp expect actual
>  	'
>
> +	test_expect_success "counting objects via bitmap ($state)" '
> +		git rev-list --count --objects HEAD >expect &&
> +		git rev-list --use-bitmap-index --count --objects HEAD >actual &&
> +		test_cmp expect actual
> +	'
> +
>  	test_expect_success "enumerate --objects ($state)" '
>  		git rev-list --objects --use-bitmap-index HEAD >tmp &&
>  		cut -d" " -f1 <tmp >tmp2 &&
> --
> 2.25.0.796.gcc29325708

Your tests look good to me, too.

Thanks,
Taylor