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

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>

diff --git a/compat/win32mmap.c b/compat/win32mmap.c
index 3a39f0fadc7ecb9871a9a85fd6d07ee67419bca8..b836169b3ce88d2967b52fa4e3a697f895dc1a13 100644 (file)
--- 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");