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| author | Michael S. Tsirkin <mst@redhat.com> | 2009-09-22 02:03:52 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-09-22 16:17:42 +0200 |
| commit | f68e14805085972b4e0b0ab684af37f713b9c262 (patch) | |
| tree | 6e0cc9e1e3f29b36ec3d7acfaf863cf9bb39ea5b | |
| parent | mm: move use_mm/unuse_mm from aio.c to mm/ (diff) | |
| download | linux-f68e14805085972b4e0b0ab684af37f713b9c262.tar.xz linux-f68e14805085972b4e0b0ab684af37f713b9c262.zip | |
mm: reduce atomic use on use_mm fast path
When the mm being switched to matches the active mm, we don't need to
increment and then drop the mm count. In a simple benchmark this happens
in about 50% of time. Making that conditional reduces contention on that
cacheline on SMP systems.
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/mmu_context.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/mm/mmu_context.c b/mm/mmu_context.c index fd473b51c903..ded9081f4021 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm) task_lock(tsk); active_mm = tsk->active_mm; - atomic_inc(&mm->mm_count); + if (active_mm != mm) { + atomic_inc(&mm->mm_count); + tsk->active_mm = mm; + } tsk->mm = mm; - tsk->active_mm = mm; switch_mm(active_mm, mm, tsk); task_unlock(tsk); - mmdrop(active_mm); + if (active_mm != mm) + mmdrop(active_mm); } /* |