Commit f68e1480 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Linus Torvalds

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: default avatarAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3d2d827f
......@@ -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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