The patch titled
mmap: avoid unnecessary anon_vma lock
has been added to the -mm tree. Its filename is
mmap-avoid-unnecessary-anon_vma-lock.patch
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------------------------------------------------------
Subject: mmap: avoid unnecessary anon_vma lock
From: Shaohua Li <shaohua.li@xxxxxxxxx>
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@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/mmap.c~mmap-avoid-unnecessary-anon_vma-lock mm/mmap.c
--- a/mm/mmap.c~mmap-avoid-unnecessary-anon_vma-lock
+++ a/mm/mmap.c
@@ -605,7 +605,7 @@ again: remove_next = 1 + (end > next->
* 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);
}
_
Patches currently in -mm which might be from shaohua.li@xxxxxxxxx are
origin.patch
mmap-avoid-unnecessary-anon_vma-lock.patch
mm-batch-activate_page-to-reduce-lock-contention.patch
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