Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756109Ab1DKVyN (ORCPT ); Mon, 11 Apr 2011 17:54:13 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38078 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751986Ab1DKVyM (ORCPT ); Mon, 11 Apr 2011 17:54:12 -0400 Date: Mon, 11 Apr 2011 14:53:24 -0700 From: Andrew Morton To: KOSAKI Motohiro Cc: Andrey Vagin , Minchan Kim , KAMEZAWA Hiroyuki , "Luis Claudio R. Goncalves" , LKML , linux-mm , David Rientjes , Oleg Nesterov , Linus Torvalds Subject: Re: [PATCH 1/4] vmscan: all_unreclaimable() use zone->all_unreclaimable as a name Message-Id: <20110411145324.ca790260.akpm@linux-foundation.org> In-Reply-To: <20110411143128.0070.A69D9226@jp.fujitsu.com> References: <20110411142949.006C.A69D9226@jp.fujitsu.com> <20110411143128.0070.A69D9226@jp.fujitsu.com> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2738 Lines: 68 On Mon, 11 Apr 2011 14:30:31 +0900 (JST) 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. The above is a nice analysis of the bug and how it came to be introduced. But we don't actually have a bug description! What was the observeable problem which got fixed? Such a description will help people understand the importance of the patch and will help people (eg, distros) who are looking at a user's bug report and wondering whether your patch will fix it. -- 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/