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From: Kim Gybels <kgybels@infogroep.be>
To: git@vger.kernel.org
Cc: Junio C Hamano <gitster@pobox.com>,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	Michael Haggerty <mhagger@alum.mit.edu>,
	Kim Gybels <kgybels@infogroep.be>
Subject: [PATCH] packed_ref_cache: don't use mmap() for small files
Date: Sat, 13 Jan 2018 17:11:49 +0100	[thread overview]
Message-ID: <20180113161149.9564-1-kgybels@infogroep.be> (raw)

Take a hint from commit ea68b0ce9f8ce8da3e360aed3cbd6720159ffbee 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 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);
 
-- 
2.15.1.windows.2


             reply	other threads:[~2018-01-13 16:18 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-13 16:11 Kim Gybels [this message]
2018-01-13 18:56 ` [PATCH] packed_ref_cache: don't use mmap() for small files 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
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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