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mmap(win32): avoid copy-on-write when it is unnecessary

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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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Johannes Schindelin 2016-04-22 16:31:26 +02:00 committed by Junio C Hamano
parent 6a730e10a7
commit 7ce7ee2d82
1 changed files with 3 additions and 2 deletions
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5
compat/win32mmap.c
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@ -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"); die("Invalid usage of mmap when built with USE_WIN32_MMAP");
hmap = CreateFileMapping((HANDLE)_get_osfhandle(fd), NULL, hmap = CreateFileMapping((HANDLE)_get_osfhandle(fd), NULL,
PAGE_WRITECOPY, 0, 0, NULL); prot == PROT_READ ? PAGE_READONLY : PAGE_WRITECOPY, 0, 0, NULL);
if (!hmap) { if (!hmap) {
errno = EINVAL; errno = EINVAL;
return MAP_FAILED; 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)) if (!CloseHandle(hmap))
warning("unable to close file mapping handle"); warning("unable to close file mapping handle");