From: Michael S. Tsirkin Date: Tue, 22 Sep 2009 00:03:52 +0000 (-0700) Subject: mm: reduce atomic use on use_mm fast path X-Git-Tag: Ubuntu-5.2.0-15.16~28012 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=f68e14805085972b4e0b0ab684af37f713b9c262;p=mirror_ubuntu-eoan-kernel.git 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 Signed-off-by: Michael S. Tsirkin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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); } /*