Re: [PATCH] revert & cherry-pick: run git gc --auto

[Phillip Wood <phillip.wood@talktalk.net>]

Hi Ævar
On 11/10/2018 11:08, Ævar Arnfjörð Bjarmason wrote:
> 
> On Thu, Oct 11 2018, Phillip Wood wrote:
> 
>> Hi Ævar
>>
>> On 10/10/2018 20:35, Ævar Arnfjörð Bjarmason wrote:
>>> Expand on the work started in 095c741edd ("commit: run git gc --auto
>>> just before the post-commit hook", 2018-02-28) to run "gc --auto" in
>>> more commands where new objects can be created.
>>>
>>> The notably missing commands are now "rebase" and "stash". Both are
>>> being rewritten in C, so any use of "gc --auto" there can wait for
>>> that.
>>
>> If cherry-pick, revert or 'rebase -i' edit the commit message then they
>> fork 'git commit' so gc --auto will be run there anyway.
> 
> Yeah it seems I totally screwed up the testing for this patch, first it
> doesn't even compile because I'm not including run-command.h, I *did*
> fix that, but while wrangling a few things didn't commit that *sigh*.
> 
> And yeah, there's some invocations where we now run gc --auto twice,
> i.e. if you do revert, but not revert --no-edit, and not on cherry-pick,
> but on cherry-pick --edit.
> 
> So yeah, this really needs to be re-thought.
> 
>> I wonder if it would be better to call 'gc --auto' from sequencer.c at
>> the end of a string of successful picks, that would cover cherry-pick,
>> 'rebase -iu' and revert. With 'rebase -i' it might be nice to avoid
>> calling 'gc --auto' until the very end, rather than every time we stop
>> for an edit but that is probably more trouble than it is worth.
> 
> That seems a lot better indeed. I.e. running it from the sequencer. I do
> wonder if there should be some smarts about running it in the middle of
> a sequence, i.e. think of a case where we're rebasing 10k commits, which
> is a gc need similar to what happens in the middle of "git svn
> clone". So maybe something where we gc --auto in the sequencer for every
> Nth commit, and at the end.

That sounds like a good idea. It would be nice if need_to_gc() was in 
libgit, then we could avoid the cost of forking unless we actually need 
to gc. Looking at builtin/gc.c there seem to be quite a few global 
variables so transforming it to library code may not be that straight 
forward.

Best Wishes

Phillip

>>
>>>
>>> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
>>> ---
>>>
>>> After reading the "Users are encouraged to run this task..." paragraph
>>> in the git-gc manpage I was wondering if due to gc --auto all over the
>>> place now (including recently in git-commit with a patch of mine) if
>>> we shouldn't change that advice.
>>>
>>> I'm meaning to send some doc changes to git-gc.txt, but in the
>>> meantime let's address this low-hanging fruit of running gc --auto
>>> when we revert or cherry-pick commits, which can like git-commit
>>> create a significant amount of loose objects.
>>>
>>>   builtin/revert.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/builtin/revert.c b/builtin/revert.c
>>> index 9a66720cfc..1b20902910 100644
>>> --- a/builtin/revert.c
>>> +++ b/builtin/revert.c
>>> @@ -209,6 +209,7 @@ int cmd_revert(int argc, const char **argv, const char *prefix)
>>>   {
>>>   	struct replay_opts opts = REPLAY_OPTS_INIT;
>>>   	int res;
>>> +	const char *argv_gc_auto[] = {"gc", "--auto", NULL};
>>>
>>>   	if (isatty(0))
>>>   		opts.edit = 1;
>>> @@ -217,6 +218,7 @@ int cmd_revert(int argc, const char **argv, const char *prefix)
>>>   	res = run_sequencer(argc, argv, &opts);
>>>   	if (res < 0)
>>>   		die(_("revert failed"));
>>> +	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
>>>   	return res;
>>>   }
>>>
>>> @@ -224,11 +226,13 @@ int cmd_cherry_pick(int argc, const char **argv, const char *prefix)
>>>   {
>>>   	struct replay_opts opts = REPLAY_OPTS_INIT;
>>>   	int res;
>>> +	const char *argv_gc_auto[] = {"gc", "--auto", NULL};
>>>
>>>   	opts.action = REPLAY_PICK;
>>>   	sequencer_init_config(&opts);
>>>   	res = run_sequencer(argc, argv, &opts);
>>>   	if (res < 0)
>>>   		die(_("cherry-pick failed"));
>>> +	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
>>>   	return res;
>>>   }
>>>