From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752961AbZH0QKu (ORCPT ); Thu, 27 Aug 2009 12:10:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752946AbZH0QKt (ORCPT ); Thu, 27 Aug 2009 12:10:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39667 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752937AbZH0QKr (ORCPT ); Thu, 27 Aug 2009 12:10:47 -0400 Date: Thu, 27 Aug 2009 19:07:20 +0300 From: "Michael S. Tsirkin" 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 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: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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