From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756298Ab3JGRYq (ORCPT ); Mon, 7 Oct 2013 13:24:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753288Ab3JGRYp (ORCPT ); Mon, 7 Oct 2013 13:24:45 -0400 Message-ID: <5252EE4A.1060904@redhat.com> Date: Mon, 07 Oct 2013 13:24:26 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Mel Gorman CC: Peter Zijlstra , Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML Subject: Re: [PATCH 13/63] sched: numa: Mitigate chance that same task always updates PTEs References: <1381141781-10992-1-git-send-email-mgorman@suse.de> <1381141781-10992-14-git-send-email-mgorman@suse.de> In-Reply-To: <1381141781-10992-14-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/07/2013 06:28 AM, Mel Gorman wrote: > From: Peter Zijlstra > > With a trace_printk("working\n"); right after the cmpxchg in > task_numa_work() we can see that of a 4 thread process, its always the > same task winning the race and doing the protection change. > > This is a problem since the task doing the protection change has a > penalty for taking faults -- it is busy when marking the PTEs. If its > always the same task the ->numa_faults[] get severely skewed. > > Avoid this by delaying the task doing the protection change such that > it is unlikely to win the privilege again. > Signed-off-by: Peter Zijlstra > Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel -- All rights reversed