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 ESMTP id CDAE58D003B for ; Mon, 11 Apr 2011 21:04:23 -0400 (EDT) Received: from m4.gw.fujitsu.co.jp (unknown [10.0.50.74]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id 64DB83EE0C0 for ; Tue, 12 Apr 2011 10:04:18 +0900 (JST) Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 3F7D12E68E5 for ; Tue, 12 Apr 2011 10:04:18 +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 0935D45DE52 for ; Tue, 12 Apr 2011 10:04:17 +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 E9BBAE7800C for ; Tue, 12 Apr 2011 10:04:16 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.240.81.145]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 98DE6E78005 for ; Tue, 12 Apr 2011 10:04:16 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 1/4] vmscan: all_unreclaimable() use zone->all_unreclaimable as a name In-Reply-To: <20110411145324.ca790260.akpm@linux-foundation.org> References: <20110411143128.0070.A69D9226@jp.fujitsu.com> <20110411145324.ca790260.akpm@linux-foundation.org> Message-Id: <20110412100417.43F2.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Tue, 12 Apr 2011 10:04:15 +0900 (JST) Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: kosaki.motohiro@jp.fujitsu.com, Andrey Vagin , Minchan Kim , KAMEZAWA Hiroyuki , "Luis Claudio R. Goncalves" , LKML , linux-mm , David Rientjes , Oleg Nesterov , Linus Torvalds Hi > > 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? The above says "Eventually, oom-killer never works". Is this no enough? The above says 1) current logic have a race 2) x86 increase a chance of the race by dma zone 3) if race is happen, oom killer don't work > > 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, 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org