From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id D03586B01B6 for ; Tue, 1 Jun 2010 02:53:20 -0400 (EDT) Received: from m4.gw.fujitsu.co.jp ([10.0.50.74]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o516rGnF024093 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 1 Jun 2010 15:53:17 +0900 Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id B39DE45DE81 for ; Tue, 1 Jun 2010 15:53:16 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 8197A45DE7E for ; Tue, 1 Jun 2010 15:53:16 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 490F71DB8037 for ; Tue, 1 Jun 2010 15:53:16 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id DD4E01DB803B for ; Tue, 1 Jun 2010 15:53:15 +0900 (JST) Date: Tue, 1 Jun 2010 15:48:24 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH] vmscan: Fix do_try_to_free_pages() return value when priority==0 reclaim failure Message-Id: <20100601154824.1d87e5a4.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100601122140.2436.A69D9226@jp.fujitsu.com> References: <20100430224316.056084208@cmpxchg.org> <20100601122140.2436.A69D9226@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Greg Thelen , Johannes Weiner , Andrew Morton , Mel Gorman , linux-mm@kvack.org, Balbir Singh List-ID: On Tue, 1 Jun 2010 12:29:41 +0900 (JST) KOSAKI Motohiro wrote: > > With this patch applied, it is possible that when do_try_to_free_pages() > > calls shrink_zones() for priority 0 that shrink_zones() may return 1 > > indicating progress, even though no pages may have been reclaimed. > > Because this is a cgroup operation, scanning_global_lru() is false and > > the following portion of do_try_to_free_pages() fails to set ret=0. > > > if (ret && scanning_global_lru(sc)) > > > ret = sc->nr_reclaimed; > > This leaves ret=1 indicating that do_try_to_free_pages() reclaimed 1 > > page even though it did not reclaim any pages. Therefore > > mem_cgroup_force_empty() erroneously believes that > > try_to_free_mem_cgroup_pages() is making progress (one page at a time), > > so there is an endless loop. > > Good catch! > > Yeah, your analysis is fine. thank you for both your testing and > making analysis. > > Unfortunatelly, this logic need more fix. because It have already been > corrupted by another regression. my point is, if priority==0 reclaim > failure occur, "ret = sc->nr_reclaimed" makes no sense at all. > > The fixing patch is here. What do you think? > > > > From 49a395b21fe1b2f864112e71d027ffcafbdc9fc0 Mon Sep 17 00:00:00 2001 > From: KOSAKI Motohiro > Date: Tue, 1 Jun 2010 11:29:50 +0900 > Subject: [PATCH] vmscan: Fix do_try_to_free_pages() return value when priority==0 reclaim failure > > Greg Thelen reported recent Johannes's stack diet patch makes kernel > hang. His test is following. > > mount -t cgroup none /cgroups -o memory > mkdir /cgroups/cg1 > echo $$ > /cgroups/cg1/tasks > dd bs=1024 count=1024 if=/dev/null of=/data/foo > echo $$ > /cgroups/tasks > echo 1 > /cgroups/cg1/memory.force_empty > > Actually, This OOM hard to try logic have been corrupted > since following two years old patch. > > commit a41f24ea9fd6169b147c53c2392e2887cc1d9247 > Author: Nishanth Aravamudan > Date: Tue Apr 29 00:58:25 2008 -0700 > > page allocator: smarter retry of costly-order allocations > > Original intention was "return success if the system have shrinkable > zones though priority==0 reclaim was failure". But the above patch > changed to "return nr_reclaimed if .....". Oh, That forgot nr_reclaimed > may be 0 if priority==0 reclaim failure. > > And Johannes's patch made more corrupt. Originally, priority==0 recliam > failure on memcg return 0, but this patch changed to return 1. It > totally confused memcg. > > This patch fixes it completely. > > Reported-by: Greg Thelen > Signed-off-by: KOSAKI Motohiro > Cc: Johannes Weiner Acked-by: KAMEZAWA Hiroyuki Thank you very much!! -- 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