From: Michael Haggerty <mhagger@alum.mit.edu>
To: Jeff King <peff@peff.net>, Kim Gybels <kgybels@infogroep.be>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: Re: [PATCH v3] packed_ref_cache: don't use mmap() for small files
Date: Sun, 21 Jan 2018 05:41:48 +0100 [thread overview]
Message-ID: <29c51594-6e29-be34-3d5f-2b9f399490f2@alum.mit.edu> (raw)
In-Reply-To: <20180117220902.GA14952@sigill.intra.peff.net>
On 01/17/2018 11:09 PM, Jeff King wrote:
> On Tue, Jan 16, 2018 at 08:38:15PM +0100, Kim Gybels wrote:
>
>> Take a hint from commit ea68b0ce9f8 (hash-object: don't use mmap() for
>> small files, 2010-02-21) and use read() instead of mmap() for small
>> packed-refs files.
>>
>> This also fixes the problem[1] where xmmap() returns NULL for zero
>> length[2], for which munmap() later fails.
>>
>> Alternatively, we could simply check for NULL before munmap(), or
>> introduce xmunmap() that could be used together with xmmap(). However,
>> always setting snapshot->buf to a valid pointer, by relying on
>> xmalloc(0)'s fallback to 1-byte allocation, makes using snapshots
>> easier.
>>
>> [1] https://github.com/git-for-windows/git/issues/1410
>> [2] Logic introduced in commit 9130ac1e196 (Better error messages for
>> corrupt databases, 2007-01-11)
>>
>> Signed-off-by: Kim Gybels <kgybels@infogroep.be>
>> ---
>>
>> Change since v2: removed separate case for zero length as suggested by Peff,
>> ensuring that snapshot->buf is always a valid pointer.
>
> Thanks, this looks fine to me (I'd be curious to hear from Michael if
> this eliminates the need for the other patches).
`snapshot->buf` can still be NULL if the `packed-refs` file didn't exist
(see the earlier code path in `load_contents()`). So either that code
path *also* has to get the `xmalloc()` treatment, or my third patch is
still necessary. (My second patch wouldn't be necessary because the
ENOENT case makes `load_contents()` return 0, triggering the early exit
from `create_snapshot()`.)
I don't have a strong preference either way.
Michael
next prev parent reply other threads:[~2018-01-21 4:41 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-13 16:11 [PATCH] packed_ref_cache: don't use mmap() for small files Kim Gybels
2018-01-13 18:56 ` Johannes Schindelin
2018-01-14 19:14 ` [PATCH v2] " Kim Gybels
2018-01-15 12:17 ` [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files" Michael Haggerty
2018-01-15 12:17 ` [PATCH 1/3] SQUASH? Mention that `snapshot::buf` can be NULL for empty files Michael Haggerty
2018-01-15 12:17 ` [PATCH 2/3] create_snapshot(): exit early if the file was empty Michael Haggerty
2018-01-15 12:17 ` [PATCH 3/3] find_reference_location(): don't invoke if `snapshot->buf` is NULL Michael Haggerty
2018-01-17 20:23 ` [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files" Johannes Schindelin
2018-01-17 21:52 ` Junio C Hamano
2018-01-15 21:15 ` [PATCH] packed_ref_cache: don't use mmap() for small files Jeff King
2018-01-15 23:37 ` Kim Gybels
2018-01-15 23:52 ` Jeff King
2018-01-16 19:38 ` [PATCH v3] " Kim Gybels
2018-01-17 22:09 ` Jeff King
2018-01-21 4:41 ` Michael Haggerty [this message]
2018-01-22 19:31 ` Junio C Hamano
2018-01-24 11:05 ` Michael Haggerty
2018-01-24 11:14 ` [PATCH 0/6] Yet another approach to handling empty snapshots Michael Haggerty
2018-01-24 11:14 ` [PATCH 1/6] struct snapshot: store `start` rather than `header_len` Michael Haggerty
2018-01-24 20:36 ` Jeff King
2018-01-24 11:14 ` [PATCH 2/6] create_snapshot(): use `xmemdupz()` rather than a strbuf Michael Haggerty
2018-01-24 11:14 ` [PATCH 3/6] find_reference_location(): make function safe for empty snapshots Michael Haggerty
2018-01-24 20:27 ` Jeff King
2018-01-24 21:11 ` Junio C Hamano
2018-01-24 21:34 ` Jeff King
2018-01-24 11:14 ` [PATCH 4/6] packed_ref_iterator_begin(): make optimization more general Michael Haggerty
2018-01-24 20:32 ` Jeff King
2018-01-24 11:14 ` [PATCH 5/6] load_contents(): don't try to mmap an empty file Michael Haggerty
2018-01-24 11:14 ` [PATCH 6/6] packed_ref_cache: don't use mmap() for small files Michael Haggerty
2018-01-24 20:38 ` [PATCH 0/6] Yet another approach to handling empty snapshots Jeff King
2018-01-24 20:54 ` Junio C Hamano
2018-02-15 16:54 ` Johannes Schindelin
2018-01-24 18:05 ` [PATCH v3] packed_ref_cache: don't use mmap() for small files Junio C Hamano
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