Re: [PATCH 4/4] mark_parents_uninteresting(): avoid most allocation
- From
Derrick Stolee <stolee@gmail.com>
- Date
- May 14, 2018, 12:47 UTC
- Message-ID
- <8447da69-d28a-433c-f324-a6380b6ca991@gmail.com>
- In-Reply-To
- <20180511180314.GD12543@sigill.intra.peff.net>
On 5/11/2018 2:03 PM, Jeff King wrote:
Show 11 quoted lines
> Commit 941ba8db57 (Eliminate recursion in setting/clearing > marks in commit list, 2012-01-14) used a clever double-loop > to avoid allocations for single-parent chains of history. > However, it did so only when following parents of parents > (which was an uncommon case), and _always_ incurred at least > one allocation to populate the list of pending parents in > the first place. > > We can turn this into zero-allocation in the common case by > iterating directly over the initial parent list, and then > following up on any pending items we might have discovered.
This change appears to improve performance, but I was unable to measure any difference between this commit and the one ahead, even when merging ds/generation-numbers (which significantly reduces the other costs). I was testing 'git status' and 'git rev-list --boundary master...origin/master' in the Linux repo with my copy of master 70,000+ commits behind origin/master.
It's still a good change, but I was hoping to find a measurable benefit :(
Show 70 quoted lines
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> Again, try "-w" for more readability.
>
> revision.c | 44 +++++++++++++++++++++++++-------------------
> 1 file changed, 25 insertions(+), 19 deletions(-)
>
> diff --git a/revision.c b/revision.c
> index 89ff9a99ce..cbe041128e 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -115,32 +115,38 @@ static void commit_stack_clear(struct commit_stack *stack)
> stack->nr = stack->alloc = 0;
> }
>
> -void mark_parents_uninteresting(struct commit *commit)
> +static void mark_one_parent_uninteresting(struct commit *commit,
> + struct commit_stack *pending)
> {
> - struct commit_stack pending = COMMIT_STACK_INIT;
> struct commit_list *l;
>
> + if (commit->object.flags & UNINTERESTING)
> + return;
> + commit->object.flags |= UNINTERESTING;
> +
> + /*
> + * Normally we haven't parsed the parent
> + * yet, so we won't have a parent of a parent
> + * here. However, it may turn out that we've
> + * reached this commit some other way (where it
> + * wasn't uninteresting), in which case we need
> + * to mark its parents recursively too..
> + */
> for (l = commit->parents; l; l = l->next)
> - commit_stack_push(&pending, l->item);
> + commit_stack_push(pending, l->item);
> +}
>
> - while (pending.nr > 0) {
> - struct commit *commit = commit_stack_pop(&pending);
> +void mark_parents_uninteresting(struct commit *commit)
> +{
> + struct commit_stack pending = COMMIT_STACK_INIT;
> + struct commit_list *l;
>
> - if (commit->object.flags & UNINTERESTING)
> - return;
> - commit->object.flags |= UNINTERESTING;
> + for (l = commit->parents; l; l = l->next)
> + mark_one_parent_uninteresting(l->item, &pending);
>
> - /*
> - * Normally we haven't parsed the parent
> - * yet, so we won't have a parent of a parent
> - * here. However, it may turn out that we've
> - * reached this commit some other way (where it
> - * wasn't uninteresting), in which case we need
> - * to mark its parents recursively too..
> - */
> - for (l = commit->parents; l; l = l->next)
> - commit_stack_push(&pending, l->item);
> - }
> + while (pending.nr > 0)
> + mark_one_parent_uninteresting(commit_stack_pop(&pending),
> + &pending);
>
> commit_stack_clear(&pending);
> }