diff options
| author | Shaohua Li <shaohua.li@intel.com> | 2011-05-25 02:11:19 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-05-25 17:39:04 +0200 |
| commit | 5f70b962ccc2f2e6259417cf3d1233dc9e16cf5e (patch) | |
| tree | 5e3d83554554e3c315a7bab654fc51345078bc9d | |
| parent | mmap: add alignment for some variables (diff) | |
| download | linux-5f70b962ccc2f2e6259417cf3d1233dc9e16cf5e.tar.xz linux-5f70b962ccc2f2e6259417cf3d1233dc9e16cf5e.zip | |
mmap: avoid unnecessary anon_vma lock
If we only change vma->vm_end, we can avoid taking anon_vma lock even if
'insert' isn't NULL, which is the case of split_vma.
As I understand it, we need the lock before because rmap must get the
'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked
to anon_vma list in __insert_vm_struct before).
But now this isn't true any more. The 'insert' VMA is already linked to
anon_vma list in __split_vma(with anon_vma_clone()) instead of
__insert_vm_struct. There is no race rmap can't get required VMAs. So
the anon_vma lock is unnecessary, and this can reduce one locking in brk
case and improve scalability.
Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/mmap.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/mmap.c b/mm/mmap.c index eaec3df82a2b..15b1fae57efe 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -609,7 +609,7 @@ again: remove_next = 1 + (end > next->vm_end); * lock may be shared between many sibling processes. Skipping * the lock for brk adjustments makes a difference sometimes. */ - if (vma->anon_vma && (insert || importer || start != vma->vm_start)) { + if (vma->anon_vma && (importer || start != vma->vm_start)) { anon_vma = vma->anon_vma; anon_vma_lock(anon_vma); } |