path: root/mm/mlock.c
diff options
authorMichel Lespinasse <>2011-01-13 15:46:09 -0800
committerLinus Torvalds <>2011-01-13 17:32:35 -0800
commit5ecfda041e4b4bd858d25bbf5a16c2a6c06d7272 (patch)
treee6c3e7dac64a5e45b48ab7836318752202579a17 /mm/mlock.c
parent72ddc8f72270758951ccefb7d190f364d20215ab (diff)
mlock: avoid dirtying pages and triggering writeback
When faulting in pages for mlock(), we want to break COW for anonymous or file pages within VM_WRITABLE, non-VM_SHARED vmas. However, there is no need to write-fault into VM_SHARED vmas since shared file pages can be mlocked first and dirtied later, when/if they actually get written to. Skipping the write fault is desirable, as we don't want to unnecessarily cause these pages to be dirtied and queued for writeback. Signed-off-by: Michel Lespinasse <> Cc: Hugh Dickins <> Cc: Rik van Riel <> Cc: Kosaki Motohiro <> Cc: Peter Zijlstra <> Cc: Nick Piggin <> Cc: Theodore Tso <> Cc: Michael Rubin <> Cc: Suleiman Souhlal <> Cc: Dave Chinner <> Cc: Christoph Hellwig <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/mlock.c')
1 files changed, 6 insertions, 1 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index b70919ce4f72..4f318642fbbe 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -171,7 +171,12 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
gup_flags = FOLL_TOUCH | FOLL_GET;
- if (vma->vm_flags & VM_WRITE)
+ /*
+ * We want to touch writable mappings with a write fault in order
+ * to break COW, except for shared mappings because these don't COW
+ * and we would not want to dirty them for nothing.
+ */
+ if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
gup_flags |= FOLL_WRITE;
/* We don't try to access the guard page of a stack vma */