From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 873816B005C for ; Thu, 27 Aug 2009 12:09:04 -0400 (EDT) Date: Thu, 27 Aug 2009 19:07:20 +0300 From: "Michael S. Tsirkin" Subject: [PATCHv5 2/3] mm: reduce atomic use on use_mm fast path Message-ID: <20090827160720.GC23722@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, linux-mm@kvack.org, akpm@linux-foundation.org, hpa@zytor.com, gregory.haskins@gmail.com, Rusty Russell , s.hetze@linux-ag.com List-ID: When mm switched to matches that of active mm, we don't need to increment and then drop the mm count. Making that conditional reduces contention on that cache line on SMP systems. Acked-by: Andrea Arcangeli Signed-off-by: Michael S. Tsirkin --- mm/mmu_context.c | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/mm/mmu_context.c b/mm/mmu_context.c index 9989c2f..0777654 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -27,13 +27,16 @@ 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); } EXPORT_SYMBOL_GPL(use_mm); -- 1.6.2.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org