Commit f68e1480 authored Sep 21, 2009 by Michael S. Tsirkin Committed by Linus Torvalds Sep 22, 2009

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>

parent 3d2d827f

mm/mmu_context.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -26,12 +26,15 @@ void use_mm(struct mm_struct *mm)

		task_lock(tsk);
		active_mm = tsk->active_mm;
		if (active_mm != mm) {
		atomic_inc(&mm->mm_count);
		tsk->mm = mm;
		tsk->active_mm = mm;
		}
		tsk->mm = mm;
		switch_mm(active_mm, mm, tsk);
		task_unlock(tsk);

		if (active_mm != mm)
		mmdrop(active_mm);
		}

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