From: Johannes Schindelin <johannes.schindelin@gmx.de>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, Sven Strickroth <email@cs-ware.de>
Subject: [PATCH 2/3] mmap(win32): avoid copy-on-write when it is unnecessary
Date: Fri, 22 Apr 2016 16:31:26 +0200 (CEST) [thread overview]
Message-ID: <3e2a45e60e2905f52f962604cf19a0e5e39b9b1b.1461335463.git.johannes.schindelin@gmx.de> (raw)
In-Reply-To: <cover.1461335463.git.johannes.schindelin@gmx.de>
Often we are mmap()ing read-only. In those cases, it is wasteful to map in
copy-on-write mode. Even worse: it can cause errors where we run out of
space in the page file.
So let's be extra careful to map files in read-only mode whenever
possible.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
compat/win32mmap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/compat/win32mmap.c b/compat/win32mmap.c
index 3a39f0f..b836169 100644
--- a/compat/win32mmap.c
+++ b/compat/win32mmap.c
@@ -22,14 +22,15 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
die("Invalid usage of mmap when built with USE_WIN32_MMAP");
hmap = CreateFileMapping((HANDLE)_get_osfhandle(fd), NULL,
- PAGE_WRITECOPY, 0, 0, NULL);
+ prot == PROT_READ ? PAGE_READONLY : PAGE_WRITECOPY, 0, 0, NULL);
if (!hmap) {
errno = EINVAL;
return MAP_FAILED;
}
- temp = MapViewOfFileEx(hmap, FILE_MAP_COPY, h, l, length, start);
+ temp = MapViewOfFileEx(hmap, prot == PROT_READ ?
+ FILE_MAP_READ : FILE_MAP_COPY, h, l, length, start);
if (!CloseHandle(hmap))
warning("unable to close file mapping handle");
--
2.8.1.306.gff998f2
next prev parent reply other threads:[~2016-04-22 14:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-22 14:31 [PATCH 0/3] Improve the mmap() emulation on Windows Johannes Schindelin
2016-04-22 14:31 ` [PATCH 1/3] win32mmap: set errno appropriately Johannes Schindelin
2016-04-22 14:31 ` Johannes Schindelin [this message]
2016-04-26 18:53 ` [PATCH 2/3] mmap(win32): avoid copy-on-write when it is unnecessary Johannes Sixt
2016-04-27 6:43 ` Johannes Schindelin
2016-04-27 18:51 ` Johannes Sixt
2016-04-28 8:03 ` Johannes Schindelin
2016-04-22 14:31 ` [PATCH 3/3] mmap(win32): avoid expensive fstat() call Johannes Schindelin
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