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mm: reduce atomic use on use_mm fast path

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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>
This commit is contained in:
Michael S. Tsirkin 2009-09-21 17:03:52 -07:00 committed by Linus Torvalds
parent 3d2d827f5c
commit f68e148050
1 changed files with 6 additions and 3 deletions
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9
mm/mmu_context.c
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@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm)
task_lock(tsk); task_lock(tsk);
active_mm = tsk->active_mm; 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->mm = mm;
tsk->active_mm = mm;
switch_mm(active_mm, mm, tsk); switch_mm(active_mm, mm, tsk);
task_unlock(tsk); task_unlock(tsk);
mmdrop(active_mm); if (active_mm != mm)
mmdrop(active_mm);
} }
/* /*