提交 f68e1480 编写于 作者: M Michael S. Tsirkin 提交者: 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: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
上级 3d2d827f
......@@ -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);
}
/*
......
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