From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f41.google.com (mail-pb0-f41.google.com [209.85.160.41]) by kanga.kvack.org (Postfix) with ESMTP id 9DEF66B0032 for ; Mon, 7 Oct 2013 14:39:39 -0400 (EDT) Received: by mail-pb0-f41.google.com with SMTP id rp2so7526140pbb.0 for ; Mon, 07 Oct 2013 11:39:39 -0700 (PDT) Message-ID: <5252FFD8.2020800@redhat.com> Date: Mon, 07 Oct 2013 14:39:20 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 21/63] sched: Update NUMA hinting faults once per scan References: <1381141781-10992-1-git-send-email-mgorman@suse.de> <1381141781-10992-22-git-send-email-mgorman@suse.de> In-Reply-To: <1381141781-10992-22-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Peter Zijlstra , Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML On 10/07/2013 06:28 AM, Mel Gorman wrote: > NUMA hinting fault counts and placement decisions are both recorded in the > same array which distorts the samples in an unpredictable fashion. The values > linearly accumulate during the scan and then decay creating a sawtooth-like > pattern in the per-node counts. It also means that placement decisions are > time sensitive. At best it means that it is very difficult to state that > the buffer holds a decaying average of past faulting behaviour. At worst, > it can confuse the load balancer if it sees one node with an artifically high > count due to very recent faulting activity and may create a bouncing effect. > > This patch adds a second array. numa_faults stores the historical data > which is used for placement decisions. numa_faults_buffer holds the > fault activity during the current scan window. When the scan completes, > numa_faults decays and the values from numa_faults_buffer are copied > across. > > Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel -- All rights reversed -- 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