From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 400E16B004D for ; Tue, 9 Jun 2009 05:27:41 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id n599x8va009173 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 9 Jun 2009 18:59:08 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 795CF45DE51 for ; Tue, 9 Jun 2009 18:59:08 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 3D83045DD79 for ; Tue, 9 Jun 2009 18:59:08 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 245681DB8038 for ; Tue, 9 Jun 2009 18:59:08 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id A76411DB8041 for ; Tue, 9 Jun 2009 18:59:04 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA In-Reply-To: <20090609184422.DD8B.A69D9226@jp.fujitsu.com> References: <20090609094231.GM18380@csn.ul.ie> <20090609184422.DD8B.A69D9226@jp.fujitsu.com> Message-Id: <20090609185036.DD8E.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Tue, 9 Jun 2009 18:59:03 +0900 (JST) Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Mel Gorman , Rik van Riel , Christoph Lameter , yanmin.zhang@intel.com, Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML List-ID: > > > > 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 -- 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