From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id ECAF96B01F7 for ; Thu, 23 Jun 2011 07:58:58 -0400 (EDT) Date: Thu, 23 Jun 2011 13:58:55 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: preallocate page before lock_page at filemap COW. (WasRe: [PATCH V2] mm: Do not keep page locked during page fault while charging it for memcg Message-ID: <20110623115855.GF31593@tiehlicka.suse.cz> References: <20110622120635.GB14343@tiehlicka.suse.cz> <20110622121516.GA28359@infradead.org> <20110622123204.GC14343@tiehlicka.suse.cz> <20110623150842.d13492cd.kamezawa.hiroyu@jp.fujitsu.com> <20110623074133.GA31593@tiehlicka.suse.cz> <20110623170811.16f4435f.kamezawa.hiroyu@jp.fujitsu.com> <20110623090204.GE31593@tiehlicka.suse.cz> <20110623190157.1bc8cbb9.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110623190157.1bc8cbb9.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Rik van Riel , Michel Lespinasse , Mel Gorman , Lutz Vieweg On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote: > On Thu, 23 Jun 2011 11:02:04 +0200 > Michal Hocko wrote: > > > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote: > > > On Thu, 23 Jun 2011 09:41:33 +0200 > > > Michal Hocko wrote: > > [...] > > > > Other than that: > > > > Reviewed-by: Michal Hocko > > > > > > > > > > I found the page is added to LRU before charging. (In this case, > > > memcg's LRU is ignored.) I'll post a new version with a fix. > > > > Yes, you are right. I have missed that. > > This means that we might race with reclaim which could evict the COWed > > page wich in turn would uncharge that page even though we haven't > > charged it yet. > > > > Can we postpone page_add_new_anon_rmap to the charging path or it would > > just race somewhere else? > > > > I got a different idea. How about this ? > I think this will have benefit for non-memcg users under OOM, too. Could you be more specific? I do not see how preallocation which might turn out to be pointless could help under OOM. > > A concerns is VM_FAULT_RETRY case but wait-for-lock will be much heavier > than preallocation + free-for-retry cost. Preallocation is rather costly when fault handler fails (e.g. SIGBUS which is the easiest one to trigger). I am not saying this approach is bad but I think that preallocation can be much more costly than unlock, charge and lock&recheck approach. -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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