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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Christian Couder <christian.couder@gmail.com>,
	git@vger.kernel.org, Christian Couder <chriscool@tuxfamily.org>,
	Ramsay Jones <ramsay@ramsayjones.plus.com>
Subject: Re: [RFC PATCH 10/10] pack-objects: improve partial packfile reuse
Date: Wed, 2 Oct 2019 11:57:22 -0400	[thread overview]
Message-ID: <20191002155721.GD6116@sigill.intra.peff.net> (raw)
In-Reply-To: <xmqqy2yrbmqu.fsf@gitster-ct.c.googlers.com>

On Fri, Sep 13, 2019 at 08:06:01PM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > On Fri, Sep 13, 2019 at 03:29:00PM -0700, Junio C Hamano wrote:
> >
> >> This comment has nothing to do with the change, but the way the
> >> patch is presented is quite hard to follow, in that the preimage or
> >> the common context lines do not help understand what the new code is
> >> doing at all ;-)
> >> 
> >> I'll come back to the remainder of the patch later.  Thanks.
> >
> > I applaud Christian's effort to tease it out into separate patches.
> 
> Ah, no question about it.  I have a suspicion that 10/10 alone may
> still be a bit too large a ball of wax, but with all the earlier
> preparatory steps are bite-sized and trivial to see how they are
> correct.
> 
> The "way the patch is presented" comment was not at all about what
> Christian did, but was about what the diff machinery computed when
> comparing the 9th step Christian created and the final step.  In its
> attempt to find and align common context lines, it ended up finding
> blank lines and almost nothing else in the earlier part of the
> patch, not just making it harder to read the new helper function
> (i.e. the best way to read record_reused_object(), for example, is
> to look only at '+' and ' ' lines, because the '-' lines are
> irrelevant), it also made it hard to see what got discarded.

Hmm, I see the early parts of this graduated to 'next'. I'm not sure
everything there is completely correct, though. E.g. I'm not sure of the
reasoning in df75281e78 (ewah/bitmap: always allocate 2 more words,
2019-09-13).

I think the "block+1" there is actually because "block" might be "0".
Prior to 2820ed171a (ewah/bitmap: introduce bitmap_word_alloc(),
2019-09-13) from the same series, that could never be the case because
we know that we always start with at least 32 allocated words. But after
that we _could_ start with an empty word array, and allocating "block *
2" would not make forward progress.

And then the "2 more words" thing is used as justification in the next
patch, 04a32d357f (pack-bitmap: don't rely on bitmap_git->reuse_objects,
2019-09-13). I won't say that there isn't some subtle dependency there,
but I certainly don't remember any logic like that at all. ;) So I think
it might bear a little more scrutiny.

I'm sorry for being so slow on giving it a more careful review. I was
traveling for work, then playing catch-up, and am now going on vacation.
So it might be a little while yet.

-Peff

  reply	other threads:[~2019-10-02 15:57 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 [this message]
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
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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