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The nommu do_mmap expects f_op->get_unmapped_area to either succeed or return -ENOSYS for VM_MAYSHARE (e.g. private read-only) mappings. Returning addr in the non-MAP_SHARED case was completely wrong, and only happened to work because addr was 0. However, it prevented VM_MAYSHARE mappings from sharing backing with the fs cache, and forced such mappings (including shareable program text) to be copied whenever the number of mappings transitioned from 0 to 1, impacting performance and memory usage. Subsequent mappings beyond the first still correctly shared memory with the first. Instead, treat VM_MAYSHARE identically to VM_SHARED at the file ops level; do_mmap already handles the semantic differences between them. Signed-off-by: Rich Felker <dalias@libc.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Greg Ungerer <gerg@uclinux.org> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| .. | ||
| file-mmu.c | ||
| file-nommu.c | ||
| inode.c | ||
| internal.h | ||
| Makefile | ||