From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Kim Gybels <kgybels@infogroep.be>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
Michael Haggerty <mhagger@alum.mit.edu>
Subject: Re: [PATCH] packed_ref_cache: don't use mmap() for small files
Date: Sat, 13 Jan 2018 19:56:26 +0100 (STD) [thread overview]
Message-ID: <nycvar.QRO.7.76.6.1801131954380.31@ZVAVAG-6OXH6DA.rhebcr.pbec.zvpebfbsg.pbz> (raw)
In-Reply-To: <20180113161149.9564-1-kgybels@infogroep.be>
Hi,
On Sat, 13 Jan 2018, Kim Gybels wrote:
> Take a hint from commit ea68b0ce9f8ce8da3e360aed3cbd6720159ffbee and use
Maybe use
ea68b0ce9f8 (hash-object: don't use mmap() for small files,
2010-02-21)
instead of the full commit name?
> 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 an xmunmap() that could be used together with xmmap().
>
> [1] https://github.com/git-for-windows/git/issues/1410
> [2] Logic introduced in commit 9130ac1e1966adb9922e64f645730d0d45383495
>
> Signed-off-by: Kim Gybels <kgybels@infogroep.be>
> ---
> refs/packed-backend.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/refs/packed-backend.c b/refs/packed-backend.c
> index dab8a85d9a..7177e5bc2f 100644
> --- a/refs/packed-backend.c
> +++ b/refs/packed-backend.c
> @@ -455,6 +455,8 @@ static void verify_buffer_safe(struct snapshot *snapshot)
> last_line, eof - last_line);
> }
>
> +#define SMALL_FILE_SIZE (32*1024)
> +
> /*
> * Depending on `mmap_strategy`, either mmap or read the contents of
> * the `packed-refs` file into the snapshot. Return 1 if the file
> @@ -489,21 +491,21 @@ static int load_contents(struct snapshot *snapshot)
> die_errno("couldn't stat %s", snapshot->refs->path);
> size = xsize_t(st.st_size);
>
> - switch (mmap_strategy) {
> - case MMAP_NONE:
> + if (!size) {
> + snapshot->buf = NULL;
> + snapshot->eof = NULL;
> + snapshot->mmapped = 0;
> + } else if (size <= SMALL_FILE_SIZE || mmap_strategy == MMAP_NONE) {
> snapshot->buf = xmalloc(size);
> bytes_read = read_in_full(fd, snapshot->buf, size);
> if (bytes_read < 0 || bytes_read != size)
> die_errno("couldn't read %s", snapshot->refs->path);
> snapshot->eof = snapshot->buf + size;
> snapshot->mmapped = 0;
> - break;
> - case MMAP_TEMPORARY:
> - case MMAP_OK:
> + } else {
> snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
> snapshot->eof = snapshot->buf + size;
> snapshot->mmapped = 1;
> - break;
> }
> close(fd);
Nicely explained, and nicely solved, for a potential extra performance
benefit ;-)
Thank you!
Dscho
next prev parent reply other threads:[~2018-01-13 18:56 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 [this message]
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
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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