[PATCH 2/3] mmap(win32): avoid copy-on-write when it is unnecessary
- From
Johannes Schindelin <johannes.schindelin@gmx.de>
- Date
- Apr 22, 2016, 14:31 UTC
- Message-ID
- <3e2a45e60e2905f52f962604cf19a0e5e39b9b1b.1461335463.git.johannes.schindelin@gmx.de>
- 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