Re: [PATCH 1/1] gc/repack: release packs when needed

[Jeff King <peff@peff.net>]

On Thu, Jan 10, 2019 at 01:01:36PM -0800, Junio C Hamano wrote:

> > diff --git a/builtin/gc.c b/builtin/gc.c
> > index 871a56f1c5..df90fd7f51 100644
> > --- a/builtin/gc.c
> > +++ b/builtin/gc.c
> > @@ -659,8 +659,10 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
> >  
> >  	report_garbage = report_pack_garbage;
> >  	reprepare_packed_git(the_repository);
> > -	if (pack_garbage.nr > 0)
> > +	if (pack_garbage.nr > 0) {
> > +		close_all_packs(the_repository->objects);
> >  		clean_pack_garbage();
> > +	}
> 
> Closing before removing does make sense, but wouldn't we want to
> move reprepare_packed_git() after clean_pack_garbage() while at it?
> After all, the logical sequence is that we used the current set of
> packs to figure out whihch ones are garbage, then now we are about
> to discard.  We close the packs in the current set (i.e. the fix
> made in this patch), discard the garbage packs.  It would make sense
> to start using the new set (i.e. "reprepare") after all that is
> done, no?  Especially, given that the next step (write-commit-graph)
> still wants to read quite a lot of data from now the latest set of
> packfiles...

I agree that your suggested ordering makes more sense, but I don't think
it matters in practice with the current code. reprepare_packed_git()
never throws away old pack entries (and if they're mmap'd, we might even
continue to use them). So the end result is the same either way.

-Peff