Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759696AbZFIJmj (ORCPT ); Tue, 9 Jun 2009 05:42:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758845AbZFIJmc (ORCPT ); Tue, 9 Jun 2009 05:42:32 -0400 Received: from gir.skynet.ie ([193.1.99.77]:37558 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754295AbZFIJmc (ORCPT ); Tue, 9 Jun 2009 05:42:32 -0400 Date: Tue, 9 Jun 2009 10:42:31 +0100 From: Mel Gorman To: KOSAKI Motohiro Cc: Rik van Riel , Christoph Lameter , yanmin.zhang@intel.com, Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML 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: <20090609094231.GM18380@csn.ul.ie> References: <20090609143211.DD64.A69D9226@jp.fujitsu.com> <20090609081821.GE18380@csn.ul.ie> <20090609173011.DD7F.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20090609173011.DD7F.A69D9226@jp.fujitsu.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3132 Lines: 87 On Tue, Jun 09, 2009 at 05:45:02PM +0900, KOSAKI Motohiro wrote: > Hi > > > > > @@ -1192,6 +1192,15 @@ static struct ctl_table vm_table[] = { > > > > .extra1 = &zero, > > > > }, > > > > { > > > > + .ctl_name = CTL_UNNUMBERED, > > > > + .procname = "zone_reclaim_interval", > > > > + .data = &zone_reclaim_interval, > > > > + .maxlen = sizeof(zone_reclaim_interval), > > > > + .mode = 0644, > > > > + .proc_handler = &proc_dointvec_jiffies, > > > > + .strategy = &sysctl_jiffies, > > > > + }, > > > > > > hmmm, I think nobody can know proper interval settings on his own systems. > > > I agree with Wu. It can be hidden. > > > > > > > For the few users that case, I expect the majority of those will choose > > either 0 or the default value of 30. They might want to alter this while > > setting zone_reclaim_mode if they don't understand the different values > > it can have for example. > > > > My preference would be that this not exist at all but the > > scan-avoidance-heuristic has to be perfect to allow that. > > Ah, I didn't concern interval==0. thanks. > I can ack this now, but please add documentation about interval==0 meaning? > I will. > > > > > > > @@ -2414,6 +2426,16 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > > > > ret = __zone_reclaim(zone, gfp_mask, order); > > > > zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); > > > > > > > > + if (!ret) { > > > > + /* > > > > + * We were unable to reclaim enough pages to stay on node and > > > > + * unable to detect in advance that the scan would fail. Allow > > > > + * off node accesses for zone_reclaim_inteval jiffies before > > > > + * trying zone_reclaim() again > > > > + */ > > > > + zone->zone_reclaim_failure = jiffies; > > > > > > Oops, this simple assignment don't care jiffies round-trip. > > > > > > > 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. > I think. > > > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/