From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id E159F60021B for ; Tue, 8 Dec 2009 20:04:25 -0500 (EST) Date: Tue, 8 Dec 2009 17:04:19 -0800 From: Chris Wright Subject: Re: [PATCH 2/9] ksm: let shared pages be swappable Message-ID: <20091209010419.GG28655@x200.localdomain> References: <20091202125501.GD28697@random.random> <20091203134610.586E.A69D9226@jp.fujitsu.com> <20091204135938.5886.A69D9226@jp.fujitsu.com> <20091204141617.f4c491e7.kamezawa.hiroyu@jp.fujitsu.com> <20091204171640.GE19624@x200.localdomain> <20091209094331.a1f53e6d.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091209094331.a1f53e6d.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Chris Wright , KOSAKI Motohiro , Andrea Arcangeli , Rik van Riel , Hugh Dickins , Andrew Morton , Izik Eidus , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: * KAMEZAWA Hiroyuki (kamezawa.hiroyu@jp.fujitsu.com) wrote: > On Fri, 4 Dec 2009 09:16:40 -0800 > Chris Wright wrote: > > * KAMEZAWA Hiroyuki (kamezawa.hiroyu@jp.fujitsu.com) wrote: > > > Hmm, can't we use ZERO_PAGE we have now ? > > > If do so, > > > - no mapcount check > > > - never on LRU > > > - don't have to maintain shared information because ZERO_PAGE itself has > > > copy-on-write nature. > > > > It's a somewhat special case, but wouldn't it be useful to have a generic > > method to recognize this kind of sharing since it's a generic issue? > > I just remembered that why ZERO_PAGE was removed (in past). It was becasue > cache-line ping-pong at fork beacause of page->mapcount. And KSM introduces > zero-pages which have mapcount again. If no problems in realitsitc usage of > KVM, ignore me. KVM is not exactly fork heavy (although it's not the only possible user of KSM). And the CoW path has fault + copy already. Semi-related...it can make good sense to make the KSM trees per NUMA node. Would mean things like page of zeroes would collapse to number of NUMA nodes pages rather than a single page, but has the benefit of not adding remote access (although, probably more useful for text pages than zero pages). thanks, -chris -- 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