Subject: Re: [GSoC Patch 2/3] commit: convert commit->generation to a slab

From: [email-masked] (Jakub Narębski)
Date: Sun, 07 Jun 2020 00:03:38 +0200

Abhishek Kumar <[email-masked]> writes:

> In this commit, we will use the generation slab helpers introduced in
> last commit and replace existing uses of commit->generation using
> 'contrib/coccinelle/generation.cocci'
>
> Signed-off-by: Abhishek Kumar <[email-masked]>
> ---
>  alloc.c                             |  1 -
>  blame.c                             |  2 +-
>  commit-graph.c                      | 39 +++++++++++-----------
>  commit-reach.c                      | 50 ++++++++++++++---------------
>  commit.c                            |  4 +--
>  commit.h                            |  1 -
>  contrib/coccinelle/generation.cocci | 12 +++++++
>  revision.c                          | 16 ++++-----
>  8 files changed, 68 insertions(+), 57 deletions(-)
>  create mode 100644 contrib/coccinelle/generation.cocci
>

For easier review I have changed the order of files, grouping together
different categories of changes.

First category is removing commit->generation and related changes:

> diff --git a/commit.h b/commit.h
> index cc610400d5..01e1c4c3eb 100644
> --- a/commit.h
> +++ b/commit.h
> @@ -34,7 +34,6 @@ struct commit {
>  	 */
>  	struct tree *maybe_tree;
>  	uint32_t graph_pos;
> -	uint32_t generation;
>  	unsigned int index;
>  };
>  

This is quite straightforward.

> diff --git a/alloc.c b/alloc.c
> index 1c64c4dd16..cbed187094 100644
> --- a/alloc.c
> +++ b/alloc.c
> @@ -109,7 +109,6 @@ void init_commit_node(struct repository *r, struct commit *c)
>  	c->object.type = OBJ_COMMIT;
>  	c->index = alloc_commit_index(r);
>  	c->graph_pos = COMMIT_NOT_FROM_GRAPH;
> -	c->generation = GENERATION_NUMBER_INFINITY;
>  }
>  
>  void *alloc_commit_node(struct repository *r)

But this change might need a more detailed write-up in the commit
message.

If I understand it correctly, this is function is used by generic commit
allocator, and given commit object may not need generation number. That
is why the default value of GENERATION_NUMBER_INFINITY is handled by new
"getters" and "setters", i.e. generation() and set_generation() -- which
are called only if commit-graph is present, I think.

The generation() returns GENERATION_NUMBER_INFINITY for commits not in
generation_slab, assuming that for all commits in the commit graph it
would be filled by commit-graph parsing -- just like init_commit_node()
would initialize commit->generation to this value.

Because <slabname>_at() (including generation_slab_at()) extends array
if necessary, we want all data on generation_slab to be correctly
initialized to GENERATION_NUMBER_INFINITY, just like init_commit_node()
would do it, because generation() "getter" cannot.  The commit might be
present on generation_slab just because allocation is done in chunks
(slabs).

Second category is semantic patch that generates the rest of changes
(which could be adjusted manually in subsequent commits).

> diff --git a/contrib/coccinelle/generation.cocci b/contrib/coccinelle/generation.cocci
> new file mode 100644
> index 0000000000..da13c44856
> --- /dev/null
> +++ b/contrib/coccinelle/generation.cocci
> @@ -0,0 +1,12 @@
> +@@
> +struct commit *c;
> +expression E;
> +@@
> +- c->generation = E
> ++ set_generation(c, E)
> +
> +@@
> +struct commit *c;
> +@@
> +- c->generation
> ++ generation(c)

I wonder if Coccinelle is able to automatically discard extra
parentheses (the problem noticed by Stolee in his reply) with the
following chunk:

  +@@
  +struct commit *c;
  +@@
  +- (c)->generation
  ++ generation(c)

Third category is all the changes that are just straight mechanical
changes being the result of applying the Coccinelle patch.

> diff --git a/blame.c b/blame.c
> index da7e28800e..50e6316076 100644
> --- a/blame.c
> +++ b/blame.c
> @@ -1272,7 +1272,7 @@ static int maybe_changed_path(struct repository *r,
>  	if (!bd)
>  		return 1;
>  
> -	if (origin->commit->generation == GENERATION_NUMBER_INFINITY)
> +	if (generation(origin->commit) == GENERATION_NUMBER_INFINITY)
>  		return 1;
>  
>  	filter = get_bloom_filter(r, origin->commit, 0);
> diff --git a/commit-graph.c b/commit-graph.c
> index 63f419048d..9ce7d4acb1 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -120,9 +120,9 @@ static int commit_gen_cmp(const void *va, const void *vb)
>  	const struct commit *b = *(const struct commit **)vb;
>  
>  	/* lower generation commits first */
> -	if (a->generation < b->generation)
> +	if (generation(a) < generation(b))
>  		return -1;
> -	else if (a->generation > b->generation)
> +	else if (generation(a) > generation(b))
>  		return 1;
>  
>  	/* use date as a heuristic when generations are equal */
> @@ -712,7 +712,7 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g,
>  	lex_index = pos - g->num_commits_in_base;
>  	commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * lex_index;
>  	item->graph_pos = pos;
> -	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
> +	set_generation(item, get_be32(commit_data + g->hash_len + 8) >> 2);
>  }
>  
>  static inline void set_commit_tree(struct commit *c, struct tree *t)
> @@ -754,7 +754,7 @@ static int fill_commit_in_graph(struct repository *r,
>  	date_low = get_be32(commit_data + g->hash_len + 12);
>  	item->date = (timestamp_t)((date_high << 32) | date_low);
>  
> -	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
> +	set_generation(item, get_be32(commit_data + g->hash_len + 8) >> 2);
>  
>  	pptr = &item->parents;
>  
> @@ -1048,7 +1048,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
>  		else
>  			packedDate[0] = 0;
>  
> -		packedDate[0] |= htonl((*list)->generation << 2);
> +		packedDate[0] |= htonl(generation((*list)) << 2);
>  
>  		packedDate[1] = htonl((*list)->date);
>  		hashwrite(f, packedDate, 8);
> @@ -1280,8 +1280,8 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
>  					ctx->commits.nr);
>  	for (i = 0; i < ctx->commits.nr; i++) {
>  		display_progress(ctx->progress, i + 1);
> -		if (ctx->commits.list[i]->generation != GENERATION_NUMBER_INFINITY &&
> -		    ctx->commits.list[i]->generation != GENERATION_NUMBER_ZERO)
> +		if (generation(ctx->commits.list[i]) != GENERATION_NUMBER_INFINITY &&
> +		    generation(ctx->commits.list[i]) != GENERATION_NUMBER_ZERO)
>  			continue;
>  
>  		commit_list_insert(ctx->commits.list[i], &list);
> @@ -1292,22 +1292,23 @@ 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 (parent->item->generation == GENERATION_NUMBER_INFINITY ||
> -				    parent->item->generation == GENERATION_NUMBER_ZERO) {
> +				if (generation(parent->item) == GENERATION_NUMBER_INFINITY ||
> +				    generation(parent->item) == GENERATION_NUMBER_ZERO) {
>  					all_parents_computed = 0;
>  					commit_list_insert(parent->item, &list);
>  					break;
> -				} else if (parent->item->generation > max_generation) {
> -					max_generation = parent->item->generation;
> +				} else if (generation(parent->item) > max_generation) {
> +					max_generation = generation(parent->item);
>  				}
>  			}

Here generation(parent->item) is called three times, which is probably
cost effective to save the value to the local variable (as Stolee
noticed).

>  
>  			if (all_parents_computed) {
> -				current->generation = max_generation + 1;
> +				set_generation(current, max_generation + 1);
>  				pop_commit(&list);
>  
> -				if (current->generation > GENERATION_NUMBER_MAX)
> -					current->generation = GENERATION_NUMBER_MAX;
> +				if (generation(current) > GENERATION_NUMBER_MAX)
> +					set_generation(current,
> +						       GENERATION_NUMBER_MAX);
>  			}
>  		}
>  	}
> @@ -2314,8 +2315,8 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags)
>  					     oid_to_hex(&graph_parents->item->object.oid),
>  					     oid_to_hex(&odb_parents->item->object.oid));
>  
> -			if (graph_parents->item->generation > max_generation)
> -				max_generation = graph_parents->item->generation;
> +			if (generation(graph_parents->item) > max_generation)
> +				max_generation = generation(graph_parents->item);
>  
>  			graph_parents = graph_parents->next;
>  			odb_parents = odb_parents->next;
> @@ -2325,7 +2326,7 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags)
>  			graph_report(_("commit-graph parent list for commit %s terminates early"),
>  				     oid_to_hex(&cur_oid));
>  
> -		if (!graph_commit->generation) {
> +		if (!generation(graph_commit)) {
>  			if (generation_zero == GENERATION_NUMBER_EXISTS)
>  				graph_report(_("commit-graph has generation number zero for commit %s, but non-zero elsewhere"),
>  					     oid_to_hex(&cur_oid));
> @@ -2345,10 +2346,10 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags)
>  		if (max_generation == GENERATION_NUMBER_MAX)
>  			max_generation--;
>  
> -		if (graph_commit->generation != max_generation + 1)
> +		if (generation(graph_commit) != max_generation + 1)
>  			graph_report(_("commit-graph generation for commit %s is %u != %u"),
>  				     oid_to_hex(&cur_oid),
> -				     graph_commit->generation,
> +				     generation(graph_commit),
>  				     max_generation + 1);
>  
>  		if (graph_commit->date != odb_commit->date)
> diff --git a/commit-reach.c b/commit-reach.c
> index 4ca7e706a1..77c980054a 100644
> --- a/commit-reach.c
> +++ b/commit-reach.c
> @@ -59,13 +59,13 @@ static struct commit_list *paint_down_to_common(struct repository *r,
>  		struct commit_list *parents;
>  		int flags;
>  
> -		if (min_generation && commit->generation > last_gen)
> +		if (min_generation && generation(commit) > last_gen)
>  			BUG("bad generation skip %8x > %8x at %s",
> -			    commit->generation, last_gen,
> +			    generation(commit), last_gen,
>  			    oid_to_hex(&commit->object.oid));
> -		last_gen = commit->generation;
> +		last_gen = generation(commit);
>  
> -		if (commit->generation < min_generation)
> +		if (generation(commit) < min_generation)
>  			break;

Here generation(commit) is called three times (two times in the
exceptional case).

>  
>  		flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
> @@ -176,7 +176,7 @@ static int remove_redundant(struct repository *r, struct commit **array, int cnt
>  		repo_parse_commit(r, array[i]);
>  	for (i = 0; i < cnt; i++) {
>  		struct commit_list *common;
> -		uint32_t min_generation = array[i]->generation;
> +		uint32_t min_generation = generation(array[i]);
>  
>  		if (redundant[i])
>  			continue;
> @@ -186,8 +186,8 @@ static int remove_redundant(struct repository *r, struct commit **array, int cnt
>  			filled_index[filled] = j;
>  			work[filled++] = array[j];
>  
> -			if (array[j]->generation < min_generation)
> -				min_generation = array[j]->generation;
> +			if (generation(array[j]) < min_generation)
> +				min_generation = generation(array[j]);
>  		}
>  		common = paint_down_to_common(r, array[i], filled,
>  					      work, min_generation);
> @@ -323,16 +323,16 @@ int repo_in_merge_bases_many(struct repository *r, struct commit *commit,
>  	for (i = 0; i < nr_reference; i++) {
>  		if (repo_parse_commit(r, reference[i]))
>  			return ret;
> -		if (reference[i]->generation < min_generation)
> -			min_generation = reference[i]->generation;
> +		if (generation(reference[i]) < min_generation)
> +			min_generation = generation(reference[i]);
>  	}
>  
> -	if (commit->generation > min_generation)
> +	if (generation(commit) > min_generation)
>  		return ret;
>  
>  	bases = paint_down_to_common(r, commit,
>  				     nr_reference, reference,
> -				     commit->generation);
> +				     generation(commit));
>  	if (commit->object.flags & PARENT2)
>  		ret = 1;
>  	clear_commit_marks(commit, all_flags);
> @@ -467,7 +467,7 @@ static enum contains_result contains_test(struct commit *candidate,
>  	/* Otherwise, we don't know; prepare to recurse */
>  	parse_commit_or_die(candidate);
>  
> -	if (candidate->generation < cutoff)
> +	if (generation(candidate) < cutoff)
>  		return CONTAINS_NO;
>  
>  	return CONTAINS_UNKNOWN;
> @@ -492,8 +492,8 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
>  	for (p = want; p; p = p->next) {
>  		struct commit *c = p->item;
>  		load_commit_graph_info(the_repository, c);
> -		if (c->generation < cutoff)
> -			cutoff = c->generation;
> +		if (generation(c) < cutoff)
> +			cutoff = generation(c);
>  	}
>  
>  	result = contains_test(candidate, want, cache, cutoff);
> @@ -544,9 +544,9 @@ static int compare_commits_by_gen(const void *_a, const void *_b)
>  	const struct commit *a = *(const struct commit * const *)_a;
>  	const struct commit *b = *(const struct commit * const *)_b;
>  
> -	if (a->generation < b->generation)
> +	if (generation(a) < generation(b))
>  		return -1;
> -	if (a->generation > b->generation)
> +	if (generation(a) > generation(b))
>  		return 1;
>  	return 0;
>  }
> @@ -585,7 +585,7 @@ int can_all_from_reach_with_flag(struct object_array *from,
>  
>  		list[nr_commits] = (struct commit *)from_one;
>  		if (parse_commit(list[nr_commits]) ||
> -		    list[nr_commits]->generation < min_generation) {
> +		    generation(list[nr_commits]) < min_generation) {
>  			result = 0;
>  			goto cleanup;
>  		}
> @@ -621,7 +621,7 @@ int can_all_from_reach_with_flag(struct object_array *from,
>  
>  					if (parse_commit(parent->item) ||
>  					    parent->item->date < min_commit_date ||
> -					    parent->item->generation < min_generation)
> +					    generation(parent->item) < min_generation)
>  						continue;
>  
>  					commit_list_insert(parent->item, &stack);
> @@ -665,8 +665,8 @@ int can_all_from_reach(struct commit_list *from, struct commit_list *to,
>  			if (from_iter->item->date < min_commit_date)
>  				min_commit_date = from_iter->item->date;
>  
> -			if (from_iter->item->generation < min_generation)
> -				min_generation = from_iter->item->generation;
> +			if (generation(from_iter->item) < min_generation)
> +				min_generation = generation(from_iter->item);
>  		}
>  
>  		from_iter = from_iter->next;
> @@ -677,8 +677,8 @@ int can_all_from_reach(struct commit_list *from, struct commit_list *to,
>  			if (to_iter->item->date < min_commit_date)
>  				min_commit_date = to_iter->item->date;
>  
> -			if (to_iter->item->generation < min_generation)
> -				min_generation = to_iter->item->generation;
> +			if (generation(to_iter->item) < min_generation)
> +				min_generation = generation(to_iter->item);
>  		}
>  
>  		to_iter->item->object.flags |= PARENT2;
> @@ -721,8 +721,8 @@ struct commit_list *get_reachable_subset(struct commit **from, int nr_from,
>  		struct commit *c = *item;
>  
>  		parse_commit(c);
> -		if (c->generation < min_generation)
> -			min_generation = c->generation;
> +		if (generation(c) < min_generation)
> +			min_generation = generation(c);
>  
>  		if (!(c->object.flags & PARENT1)) {
>  			c->object.flags |= PARENT1;
> @@ -755,7 +755,7 @@ struct commit_list *get_reachable_subset(struct commit **from, int nr_from,
>  
>  			parse_commit(p);
>  
> -			if (p->generation < min_generation)
> +			if (generation(p) < min_generation)
>  				continue;
>  
>  			if (p->object.flags & PARENT2)
> diff --git a/commit.c b/commit.c
> index 87686a7055..8dad0f8446 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -731,9 +731,9 @@ int compare_commits_by_gen_then_commit_date(const void *a_, const void *b_, void
>  	const struct commit *a = a_, *b = b_;
>  
>  	/* newer commits first */
> -	if (a->generation < b->generation)
> +	if (generation(a) < generation(b))
>  		return 1;
> -	else if (a->generation > b->generation)
> +	else if (generation(a) > generation(b))
>  		return -1;
>  
>  	/* use date as a heuristic when generations are equal */
> diff --git a/revision.c b/revision.c
> index 60cca8c0b9..d76382007c 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -720,7 +720,7 @@ static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
>  	if (!revs->repo->objects->commit_graph)
>  		return -1;
>  
> -	if (commit->generation == GENERATION_NUMBER_INFINITY)
> +	if (generation(commit) == GENERATION_NUMBER_INFINITY)
>  		return -1;
>  
>  	filter = get_bloom_filter(revs->repo, commit, 0);
> @@ -3314,7 +3314,7 @@ static void explore_to_depth(struct rev_info *revs,
>  	struct topo_walk_info *info = revs->topo_walk_info;
>  	struct commit *c;
>  	while ((c = prio_queue_peek(&info->explore_queue)) &&
> -	       c->generation >= gen_cutoff)
> +	       generation(c) >= gen_cutoff)
>  		explore_walk_step(revs);
>  }
>  
> @@ -3330,7 +3330,7 @@ static void indegree_walk_step(struct rev_info *revs)
>  	if (parse_commit_gently(c, 1) < 0)
>  		return;
>  
> -	explore_to_depth(revs, c->generation);
> +	explore_to_depth(revs, generation(c));
>  
>  	for (p = c->parents; p; p = p->next) {
>  		struct commit *parent = p->item;
> @@ -3354,7 +3354,7 @@ static void compute_indegrees_to_depth(struct rev_info *revs,
>  	struct topo_walk_info *info = revs->topo_walk_info;
>  	struct commit *c;
>  	while ((c = prio_queue_peek(&info->indegree_queue)) &&
> -	       c->generation >= gen_cutoff)
> +	       generation(c) >= gen_cutoff)
>  		indegree_walk_step(revs);
>  }
>  
> @@ -3414,8 +3414,8 @@ static void init_topo_walk(struct rev_info *revs)
>  		test_flag_and_insert(&info->explore_queue, c, TOPO_WALK_EXPLORED);
>  		test_flag_and_insert(&info->indegree_queue, c, TOPO_WALK_INDEGREE);
>  
> -		if (c->generation < info->min_generation)
> -			info->min_generation = c->generation;
> +		if (generation(c) < info->min_generation)
> +			info->min_generation = generation(c);
>  
>  		*(indegree_slab_at(&info->indegree, c)) = 1;
>  
> @@ -3473,8 +3473,8 @@ static void expand_topo_walk(struct rev_info *revs, struct commit *commit)
>  		if (parse_commit_gently(parent, 1) < 0)
>  			continue;
>  
> -		if (parent->generation < info->min_generation) {
> -			info->min_generation = parent->generation;
> +		if (generation(parent) < info->min_generation) {
> +			info->min_generation = generation(parent);
>  			compute_indegrees_to_depth(revs, info->min_generation);
>  		}

Best,
--
Jakub Narębski