Re: [PATCH 1/6] commit-graph: fix regression when computing bloom filter

From: Abhishek Kumar <abhishekkumar8222@gmail.com>
Date: Jul 30, 2020, 05:24 UTC
Message-ID: <20200730052429.GA50429@Abhishek-Arch>
In-Reply-To: <20200728152844.GB87373@syl.lan>

On Tue, Jul 28, 2020 at 11:28:44AM -0400, Taylor Blau wrote:

Show 24 quoted lines

> On Tue, Jul 28, 2020 at 09:13:46AM +0000, Abhishek Kumar via GitGitGadget wrote:
> > From: Abhishek Kumar <abhishekkumar8222@gmail.com>
> >
> > With 3d112755 (commit-graph: examine commits by generation number), Git
> > knew to sort by generation number before examining the diff when not
> > using pack order. c49c82aa (commit: move members graph_pos, generation
> > to a slab, 2020-06-17) moved generation number into a slab and
> > introduced a helper which returns GENERATION_NUMBER_INFINITY when
> > writing the graph. Sorting is no longer useful and essentially reverts
> > the earlier commit.
> 
> This last sentence is slightly confusing. Do you think it would be more
> clear if you said elaborated a bit? Perhaps something like:
> 
>   [...]
> 
>   commit_gen_cmp is used when writing a commit-graph to sort commits in
>   generation order before computing Bloom filters. Since c49c82aa made
>   it so that 'commit_graph_generation()' returns
>   'GENERATION_NUMBER_INFINITY' during writing, we cannot call it within
>   this function. Instead, access the generation number directly through
>   the slab (i.e., by calling 'commit_graph_data_at(c)->generation') in
>   order to access it while writing.
>

Thanks! That is clearer. Will change.

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> I think the above would be a good extra paragraph in the commit message
> provided that you remove the sentence beginning with "Sorting is no
> longer useful..."
> 
> > Let's fix this by accessing generation number directly through the slab.
> >
> > Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
> > ---
> >  commit-graph.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/commit-graph.c b/commit-graph.c
> > index 1af68c297d..5d3c9bd23c 100644
> > --- a/commit-graph.c
> > +++ b/commit-graph.c
> > @@ -144,8 +144,9 @@ static int commit_gen_cmp(const void *va, const void *vb)
> >  	const struct commit *a = *(const struct commit **)va;
> >  	const struct commit *b = *(const struct commit **)vb;
> >
> > -	uint32_t generation_a = commit_graph_generation(a);
> > -	uint32_t generation_b = commit_graph_generation(b);
> > +	uint32_t generation_a = commit_graph_data_at(a)->generation;
> > +	uint32_t generation_b = commit_graph_data_at(b)->generation;
> > +
> 
> Nit; this whitespace diff is extraneous, but it's not hurting anything
> either. Since it looks like you're rerolling anyway, it would be good to
> just get rid of it.
> 
> Otherwise this fix makes sense to me.
> 
> >  	/* lower generation commits first */
> >  	if (generation_a < generation_b)
> >  		return -1;
> > --
> > gitgitgadget
> 
> Thanks,
> Taylor