From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 5FEF56B0055 for ; Tue, 9 Jun 2009 06:11:15 -0400 (EDT) Date: Tue, 9 Jun 2009 11:44:04 +0100 From: Mel Gorman Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA Message-ID: <20090609104404.GP18380@csn.ul.ie> References: <20090609094231.GM18380@csn.ul.ie> <20090609184422.DD8B.A69D9226@jp.fujitsu.com> <20090609185036.DD8E.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20090609185036.DD8E.A69D9226@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Rik van Riel , Christoph Lameter , yanmin.zhang@intel.com, Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML List-ID: On Tue, Jun 09, 2009 at 06:59:03PM +0900, KOSAKI Motohiro wrote: > > > > > Here it is just recording the jiffies value. The real smarts with the counter > > > > > use time_before() which I assumed could handle jiffie wrap-arounds. Even > > > > > if it doesn't, the consequence is that one scan will occur that could have > > > > > been avoided around the time of the jiffie wraparound. The value will then > > > > > be reset and it will be fine. > > > > > > > > time_before() assume two argument are enough nearly time. > > > > if we use 32bit cpu and HZ=1000, about jiffies wraparound about one month. > > > > > > > > Then, > > > > > > > > 1. zone reclaim failure occur > > > > 2. system works fine for one month > > > > 3. jiffies wrap and time_before() makes mis-calculation. > > > > > > > > > > And the scan occurs uselessly and zone_reclaim_failure gets set again. > > > I believe the one useless scan is not significant enough to warrent dealing > > > with jiffie wraparound. > > > > Thank you for kindful explanation. > > I fully agreed. > > Bah, no, not agreed. > simple last failure recording makes following scenario. > > > 1. zone reclaim failure occur. update zone_reclaim_failure. > ^ > | time_before() return 1, and zone_reclaim() return immediately. > v > 2. after 32 second. > ^ > | time_before() return 0, and zone_reclaim() works normally > v > 3. after one month > ^ > | time_before() return 1, and zone_reclaim() return immediately. > | although recent zone_reclaim() never failed. > v > 4. after more one month > Pants. /me slaps self + /* Watch for jiffie wraparound */ + if (unlikely(jiffies < zone->zone_reclaim_failure)) + zone->zone_reclaim_failure = jiffies; + + /* Do not attempt a scan if scanning failed recently */ + if (time_before(jiffies, + zone->zone_reclaim_failure + zone_reclaim_interval)) + return 0; + ? -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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