diff options
| author | Michel Lespinasse <[email protected]> | 2011-01-13 15:46:09 -0800 |
|---|---|---|
| committer | Linus Torvalds <[email protected]> | 2011-01-13 17:32:35 -0800 |
| commit | 5ecfda041e4b4bd858d25bbf5a16c2a6c06d7272 (patch) | |
| tree | e6c3e7dac64a5e45b48ab7836318752202579a17 | |
| parent | 72ddc8f72270758951ccefb7d190f364d20215ab (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 <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Kosaki Motohiro <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Theodore Tso <[email protected]>
Cc: Michael Rubin <[email protected]>
Cc: Suleiman Souhlal <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
| -rw-r--r-- | mm/memory.c | 7 | ||||
| -rw-r--r-- | mm/mlock.c | 7 |
2 files changed, 12 insertions, 2 deletions
diff --git a/mm/memory.c b/mm/memory.c index 9144fae9a68b..b8f97b8575b7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3299,7 +3299,12 @@ int make_pages_present(unsigned long addr, unsigned long end) vma = find_vma(current->mm, addr); if (!vma) return -ENOMEM; - write = (vma->vm_flags & VM_WRITE) != 0; + /* + * 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. + */ + write = (vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE; BUG_ON(addr >= end); BUG_ON(end > vma->vm_end); len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE; 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, VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 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 */ |