From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757692Ab1DMSsp (ORCPT ); Wed, 13 Apr 2011 14:48:45 -0400 Received: from smtp-out.google.com ([216.239.44.51]:27491 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757037Ab1DMSsn (ORCPT ); Wed, 13 Apr 2011 14:48:43 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=aBA0Xs90wJ3zkef9uk8ioRQaRjMfmzN7aOdTIzmaxGO1pi1iO40L8a6Nv9SmCxeP4V 3StqaT5ho4ij85vAkGiA== Date: Wed, 13 Apr 2011 11:48:39 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: KOSAKI Motohiro cc: Andrey Vagin , Minchan Kim , KAMEZAWA Hiroyuki , "Luis Claudio R. Goncalves" , LKML , linux-mm , Oleg Nesterov , Andrew Morton , Linus Torvalds Subject: Re: [PATCH 1/4] vmscan: all_unreclaimable() use zone->all_unreclaimable as a name In-Reply-To: <20110411143128.0070.A69D9226@jp.fujitsu.com> Message-ID: References: <20110411142949.006C.A69D9226@jp.fujitsu.com> <20110411143128.0070.A69D9226@jp.fujitsu.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 Apr 2011, KOSAKI Motohiro wrote: > all_unreclaimable check in direct reclaim has been introduced at 2.6.19 > by following commit. > > 2006 Sep 25; commit 408d8544; oom: use unreclaimable info > > And it went through strange history. firstly, following commit broke > the logic unintentionally. > > 2008 Apr 29; commit a41f24ea; page allocator: smarter retry of > costly-order allocations > > Two years later, I've found obvious meaningless code fragment and > restored original intention by following commit. > > 2010 Jun 04; commit bb21c7ce; vmscan: fix do_try_to_free_pages() > return value when priority==0 > > But, the logic didn't works when 32bit highmem system goes hibernation > and Minchan slightly changed the algorithm and fixed it . > > 2010 Sep 22: commit d1908362: vmscan: check all_unreclaimable > in direct reclaim path > > But, recently, Andrey Vagin found the new corner case. Look, > > struct zone { > .. > int all_unreclaimable; > .. > unsigned long pages_scanned; > .. > } > > zone->all_unreclaimable and zone->pages_scanned are neigher atomic > variables nor protected by lock. Therefore zones can become a state > of zone->page_scanned=0 and zone->all_unreclaimable=1. In this case, > current all_unreclaimable() return false even though > zone->all_unreclaimabe=1. > > Is this ignorable minor issue? No. Unfortunatelly, x86 has very > small dma zone and it become zone->all_unreclamble=1 easily. and > if it become all_unreclaimable=1, it never restore all_unreclaimable=0. > Why? if all_unreclaimable=1, vmscan only try DEF_PRIORITY reclaim and > a-few-lru-pages>>DEF_PRIORITY always makes 0. that mean no page scan > at all! > > Eventually, oom-killer never works on such systems. That said, we > can't use zone->pages_scanned for this purpose. This patch restore > all_unreclaimable() use zone->all_unreclaimable as old. and in addition, > to add oom_killer_disabled check to avoid reintroduce the issue of > commit d1908362. > > Reported-by: Andrey Vagin > Signed-off-by: KOSAKI Motohiro > Cc: Nick Piggin > Reviewed-by: Minchan Kim > Reviewed-by: KAMEZAWA Hiroyuki Acked-by: David Rientjes Seems like it should be a candidate for stable inclusion as well, nice catch.