From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752339AbZGMAiG (ORCPT ); Sun, 12 Jul 2009 20:38:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751315AbZGMAhy (ORCPT ); Sun, 12 Jul 2009 20:37:54 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:54995 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751228AbZGMAhy (ORCPT ); Sun, 12 Jul 2009 20:37:54 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Minchan Kim Subject: Re: [RFC PATCH 2/2] Don't continue reclaim if the system have plenty free memory Cc: kosaki.motohiro@jp.fujitsu.com, LKML , linux-mm , Andrew Morton , Rik van Riel , Wu Fengguang In-Reply-To: <28c262360907090358q7cdbd067y22b7312c489e7598@mail.gmail.com> References: <20090709140234.239F.A69D9226@jp.fujitsu.com> <28c262360907090358q7cdbd067y22b7312c489e7598@mail.gmail.com> Message-Id: <20090713092428.6249.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Mon, 13 Jul 2009 09:37:50 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Thu, Jul 9, 2009 at 2:08 PM, KOSAKI > Motohiro wrote: > >> Hi, Kosaki. > >> > >> On Tue, Jul 7, 2009 at 6:48 PM, KOSAKI > >> Motohiro wrote: > >> > Subject: [PATCH] Don't continue reclaim if the system have plenty free memory > >> > > >> > On concurrent reclaim situation, if one reclaimer makes OOM, maybe other > >> > reclaimer can stop reclaim because OOM killer makes enough free memory. > >> > > >> > But current kernel doesn't have its logic. Then, we can face following accidental > >> > 2nd OOM scenario. > >> > > >> > 1. System memory is used by only one big process. > >> > 2. memory shortage occur and concurrent reclaim start. > >> > 3. One reclaimer makes OOM and OOM killer kill above big process. > >> > 4. Almost reclaimable page will be freed. > >> > 5. Another reclaimer can't find any reclaimable page because those pages are > >> > ? already freed. > >> > 6. Then, system makes accidental and unnecessary 2nd OOM killer. > >> > > >> > >> Did you see the this situation ? > >> Why I ask is that we have already a routine for preventing parallel > >> OOM killing in __alloc_pages_may_oom. > >> > >> Couldn't it protect your scenario ? > > > > Can you please see actual code of this patch? > > I mean follow as, > > static inline struct page * > __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, > struct zonelist *zonelist, enum zone_type high_zoneidx, > ... > > > /* > * Go through the zonelist yet one more time, keep very high watermark > * here, this is only to catch a parallel oom killing, we must fail if > * we're still under heavy pressure. > */ > page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, > order, zonelist, high_zoneidx, > ALLOC_WMARK_HIGH|ALLOC_CPUSET, > preferred_zone, migratetype); Thanks, I catch your point. Yes, the issue explained my description only happen old distro kernel. I haven't notice this issue was already fixed. very thanks. but above fix doesn't make sense. it mean - concurrent reclaim can drop too many usable memory - but only gurantee it doesn't cause oom Then, I'll fix my patch description. > > Those two patches fix different problem. > > > > 1/2 fixes the issue of that concurrent direct reclaimer makes > > too many isolated pages. > > 2/2 fixes the issue of that reclaim and exit race makes accidental oom. > > > > > >> If it can't, Could you explain the scenario in more detail ? > > > > __alloc_pages_may_oom() check don't effect the threads of already > > entered reclaim. it's obvious. > > Threads which are entered into direct reclaim mode will call > __alloc_pages_may_oom before out_of_memory. > At that time, if one big process is killed a while ago, > get_page_from_freelist in __alloc_pages_may_oom will be succeeded at > last. So I think it doesn't occur OOM. > > But in that case, we suffered from unnecessary page scanning per each > priority(12~0). So in this case, your patch is good to me. then you > would be better to change log. :)