From: Michael Haggerty <mhagger@alum.mit.edu>
To: Kim Gybels <kgybels@infogroep.be>
Cc: Johannes Schindelin <johannes.schindelin@gmx.de>,
Junio C Hamano <gitster@pobox.com>,
git@vger.kernel.org, Michael Haggerty <mhagger@alum.mit.edu>
Subject: [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files"
Date: Mon, 15 Jan 2018 13:17:32 +0100 [thread overview]
Message-ID: <cover.1516017331.git.mhagger@alum.mit.edu> (raw)
In-Reply-To: <20180114191416.2368-1-kgybels@infogroep.be>
Thanks for your patch. I haven't measured the performance difference
of `mmap()` vs. `read()` for small `packed-refs` files, but it's not
surprising that `read()` would be faster.
I especially like the fix for zero-length `packed-refs` files. (Even
though AFAIK Git never writes such files, they are totally legitimate
and shouldn't cause Git to fail.) With or without the additions
mentioned below,
Reviewed-by: Michael Haggerty <mhagger@alum.mit.edu>
While reviewing your patch, I realized that some areas of the existing
code use constructs that are undefined according to the C standard,
such as computing `NULL + 0` and `NULL - NULL`. This was already wrong
(and would come up more frequently after your change). Even though
these are unlikely to be problems in the real world, it would be good
to avoid them.
So I will follow up this email with three patches:
1. Mention that `snapshot::buf` can be NULL for empty files
I suggest squashing this into your patch, to make it clear that
`snapshot::buf` and `snapshot::eof` can also be NULL if the
`packed-refs` file is empty.
2. create_snapshot(): exit early if the file was empty
Avoid undefined behavior by returning early if `snapshot->buf` is
NULL.
3. find_reference_location(): don't invoke if `snapshot->buf` is NULL
Avoid undefined behavior and confusing semantics by not calling
`find_reference_location()` when `snapshot->buf` is NULL.
Michael
Michael Haggerty (3):
SQUASH? Mention that `snapshot::buf` can be NULL for empty files
create_snapshot(): exit early if the file was empty
find_reference_location(): don't invoke if `snapshot->buf` is NULL
refs/packed-backend.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
--
2.14.2
next prev parent reply other threads:[~2018-01-15 12:17 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 ` Michael Haggerty [this message]
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
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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