From: Jonathan Tan <jonathantanmy@google.com>
To: peff@peff.net
Cc: jonathantanmy@google.com, christian.couder@gmail.com,
git@vger.kernel.org, gitster@pobox.com, chriscool@tuxfamily.org,
ramsay@ramsayjones.plus.com
Subject: Re: [RFC PATCH 10/10] pack-objects: improve partial packfile reuse
Date: Fri, 11 Oct 2019 14:04:34 -0700 [thread overview]
Message-ID: <20191011210434.140296-1-jonathantanmy@google.com> (raw)
In-Reply-To: <20191011180125.GA20601@sigill.intra.peff.net>
> > This makes sense - offsets may be different when we omit objects from
> > the packfile. I think this can be computed by calculating the number of
> > zero bits between the current object's index and the nth object prior
> > (where n is the offset) in the bitmap resulting from
> > reuse_partial_packfile_from_bitmap() above, thus eliminating the need
> > for this array, but I haven't tested it.
>
> You need to know not just the number of zero bits, but the accumulated
> offset due to those missing objects. So you'd end up having to walk over
> the revindex for that set of objects. This array is basically caching
> those accumulated offsets (for the parts we _do_ include) so we don't
> have to compute them repeatedly.
Ah...yes. For some reason I thought that the offset was a number of
objects, but it is actually a number of bytes. The patch makes sense
now.
> There's also a more subtle issue with entry sizes; see below.
Good point.
> > > @@ -1002,6 +1132,10 @@ static int have_duplicate_entry(const struct object_id *oid,
> > > {
> > > struct object_entry *entry;
> > >
> > > + if (reuse_packfile_bitmap &&
> > > + bitmap_walk_contains(bitmap_git, reuse_packfile_bitmap, oid))
> > > + return 1;
> >
> > Hmm...why did we previously not need to check the reuse information, but
> > we do now? I gave the code a cursory glance but couldn't find the
> > answer.
>
> I think the original code may simply have been buggy and nobody noticed.
> Here's what I wrote when this line was added in our fork:
[snip explanation]
Thanks - I'll also take a look if I have time.
> Thanks for looking at it. I still have to take a careful pass over the
> whole split, but I've tried to at least answer your questions in the
> meantime.
Thanks for your responses. Also thanks to Christian for splitting it in
the first place, making it easier to review.
next prev parent reply other threads:[~2019-10-11 21:04 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-13 13:02 [RFC PATCH 00/10] Rewrite packfile reuse code Christian Couder
2019-09-13 13:02 ` [RFC PATCH 01/10] builtin/pack-objects: report reused packfile objects Christian Couder
2019-09-13 13:02 ` [RFC PATCH 02/10] packfile: expose get_delta_base() Christian Couder
2019-09-13 13:02 ` [RFC PATCH 03/10] ewah/bitmap: introduce bitmap_word_alloc() Christian Couder
2019-09-13 13:02 ` [RFC PATCH 04/10] ewah/bitmap: always allocate 2 more words Christian Couder
2019-10-10 23:40 ` Jonathan Tan
2019-10-11 7:49 ` Christian Couder
2019-10-11 18:05 ` Jeff King
2019-09-13 13:02 ` [RFC PATCH 05/10] pack-bitmap: don't rely on bitmap_git->reuse_objects Christian Couder
2019-10-10 23:44 ` Jonathan Tan
2019-10-11 7:50 ` Christian Couder
2019-09-13 13:02 ` [RFC PATCH 06/10] pack-bitmap: introduce bitmap_walk_contains() Christian Couder
2019-09-13 13:02 ` [RFC PATCH 07/10] csum-file: introduce hashfile_total() Christian Couder
2019-09-13 13:02 ` [RFC PATCH 08/10] pack-objects: introduce pack.allowPackReuse Christian Couder
2019-09-13 21:37 ` Junio C Hamano
2019-09-13 13:02 ` [RFC PATCH 09/10] builtin/pack-objects: introduce obj_is_packed() Christian Couder
2019-09-13 13:02 ` [RFC PATCH 10/10] pack-objects: improve partial packfile reuse Christian Couder
2019-09-13 22:29 ` Junio C Hamano
2019-09-14 2:02 ` Jeff King
2019-09-14 3:06 ` Junio C Hamano
2019-10-02 15:57 ` Jeff King
2019-10-03 2:06 ` Junio C Hamano
2019-10-03 6:55 ` Christian Couder
2019-10-10 23:59 ` Jonathan Tan
2019-10-11 7:39 ` Christian Couder
2019-10-11 18:01 ` Jeff King
2019-10-11 21:04 ` Jonathan Tan [this message]
2019-10-12 0:04 ` Junio C Hamano
2019-10-13 7:38 ` Jeff King
2019-10-17 7:03 ` Junio C Hamano
2019-10-17 7:23 ` Jeff King
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