From: Jonathan Tan <jonathantanmy@google.com>
To: christian.couder@gmail.com
Cc: git@vger.kernel.org, gitster@pobox.com, peff@peff.net,
chriscool@tuxfamily.org, ramsay@ramsayjones.plus.com,
Jonathan Tan <jonathantanmy@google.com>
Subject: Re: [RFC PATCH 04/10] ewah/bitmap: always allocate 2 more words
Date: Thu, 10 Oct 2019 16:40:40 -0700 [thread overview]
Message-ID: <20191010234040.168894-1-jonathantanmy@google.com> (raw)
In-Reply-To: <20190913130226.7449-5-chriscool@tuxfamily.org>
> From: Jeff King <peff@peff.net>
>
> In a following patch we will allocate a variable number
> of words in some bitmaps. When iterating over the words we
> will need a mark to tell us when to stop iterating. Let's
> always allocate 2 more words, that will always contain 0,
> as that mark.
[snip]
> if (block >= self->word_alloc) {
> size_t old_size = self->word_alloc;
> - self->word_alloc = block * 2;
> + self->word_alloc = (block + 1) * 2;
> REALLOC_ARRAY(self->words, self->word_alloc);
> memset(self->words + old_size, 0x0,
> (self->word_alloc - old_size) * sizeof(eword_t));
This patch set was mentioned as needing more thorough review in "What's
Cooking" [1], so I thought I'd give it a try. As Peff said [2], the
justification in the commit message looks incorrect. He suggests that it
is most likely because "block" might be 0 (which is possible because a
previous patch eliminated the minimum of 32), which makes sense to me.
In any case, the next patch does not use 0 as a sentinel mark. Iteration
stops when word_alloc is reached anyway, and since this is a regular
bitmap, 0 is a valid word and cannot be used as a sentinel. (Maybe 0 is
a valid word in a compressed EWAH bitmap too...not sure about that.)
I think this should be squashed with patch 3, adding to that commit
message "since word_alloc might be 0, we need to change the growth
function". (Or just make the minimum word_alloc be 1 or 32 or something
positive, if that's possible.)
[1] https://public-inbox.org/git/xmqq36g5444k.fsf@gitster-ct.c.googlers.com/
[2] https://public-inbox.org/git/20191002155721.GD6116@sigill.intra.peff.net/
next prev parent reply other threads:[~2019-10-10 23:40 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 [this message]
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
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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