Re: [GSOC Patch v2 3/4] commit-graph: use generation directly when writing commit-graph

From: "Jakub Narębski" <jnareb@gmail.com>
To: Abhishek Kumar <abhishekkumar8222@gmail.com>
Cc: git@vger.kernel.org, Derrick Stolee <stolee@gmail.com>
Subject: Re: [GSOC Patch v2 3/4] commit-graph: use generation directly when writing commit-graph
Date: Mon, 08 Jun 2020 18:31:49 +0200	[thread overview]
Message-ID: <85zh9dsemi.fsf@gmail.com> (raw)
In-Reply-To: <20200607193237.699335-4-abhishekkumar8222@gmail.com> (Abhishek Kumar's message of "Mon, 8 Jun 2020 01:02:36 +0530")

Abhishek Kumar <abhishekkumar8222@gmail.com> writes:

> commit_graph_generation() returns GENERATION_NUMBER_INFINITY if the
> graph position for commit is COMMIT_NOT_FROM_GRAPH.
>
> While this is true when reading from a commit graph, no graph positions
> are associated with a commit when writing a commit graph. Therefore, the
> helper incorrectly returns GENERATION_NUMBER_INFINITY despite having a
> finite generation number.
>
> Let's fix this by using generation number directly when writing a commit
> graph.

I think that to avoid having non-working patch (which can cause problems
when bisecting), it would be a better idea to switch the order of
patches 2 and 3.  This way we won't have incorrect behaviour.

>
> Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
> ---
>  commit-graph.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/commit-graph.c b/commit-graph.c
> index f7cca4def4..0dc79e7c90 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -1070,7 +1070,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
>  		else
>  			packedDate[0] = 0;
>  
> -		packedDate[0] |= htonl(commit_graph_generation((*list)) << 2);
> +		packedDate[0] |= htonl(commit_graph_data_at(*list)->generation << 2);
>

All right.

>  		packedDate[1] = htonl((*list)->date);
>  		hashwrite(f, packedDate, 8);
> @@ -1301,9 +1301,11 @@ 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 (commit_graph_generation(ctx->commits.list[i]) != GENERATION_NUMBER_INFINITY &&
> -		    commit_graph_generation(ctx->commits.list[i]) != GENERATION_NUMBER_ZERO)
> +		if (generation != GENERATION_NUMBER_INFINITY &&
> +		    generation != GENERATION_NUMBER_ZERO)
>  			continue;
>

All right; this also introduces local variable to avoid accessing the
slab twice^W four times...

>  		commit_list_insert(ctx->commits.list[i], &list);
> @@ -1314,8 +1316,9 @@ 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 (commit_graph_generation(parent->item) == GENERATION_NUMBER_INFINITY ||
> -				    commit_graph_generation(parent->item) == GENERATION_NUMBER_ZERO) {
> +
> +				if (generation == GENERATION_NUMBER_INFINITY ||
> +				    generation == GENERATION_NUMBER_ZERO) {
>  					all_parents_computed = 0;
>  					commit_list_insert(parent->item, &list);
>  					break;

... which is then used here.

Best,
-- 
Jakub Narębski