From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 7932C6B004D for ; Sat, 15 Aug 2009 23:41:14 -0400 (EDT) Date: Sun, 16 Aug 2009 11:28:22 +0800 From: Wu Fengguang Subject: Re: [RFC] respect the referenced bit of KVM guest pages? Message-ID: <20090816032822.GB6888@localhost> References: <20090805024058.GA8886@localhost> <20090805155805.GC23385@random.random> <20090806100824.GO23385@random.random> <4A7AAE07.1010202@redhat.com> <20090806102057.GQ23385@random.random> <20090806105932.GA1569@localhost> <4A7AC201.4010202@redhat.com> <20090806130631.GB6162@localhost> <4A7AD79E.4020604@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A7AD79E.4020604@redhat.com> Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: Avi Kivity , Andrea Arcangeli , "Dike, Jeffrey G" , "Yu, Wilfred" , "Kleen, Andi" , Hugh Dickins , Andrew Morton , Christoph Lameter , KOSAKI Motohiro , Mel Gorman , LKML , linux-mm List-ID: On Thu, Aug 06, 2009 at 09:16:14PM +0800, Rik van Riel wrote: > Wu Fengguang wrote: > > > I guess both schemes have unacceptable flaws. > > > > For JVM/BIGMEM workload, most pages would be found referenced _all the time_. > > So the KEEP_MOST scheme could increase reclaim overheads by N=250 times; > > while the DROP_CONTINUOUS scheme is effectively zero cost. > > The higher overhead may not be an issue on smaller systems, > or inside smaller cgroups inside large systems, when doing > cgroup reclaim. Right. > > However, the DROP_CONTINUOUS scheme does bring more _indeterminacy_. > > It can behave vastly different on single active task and multi ones. > > It is short sighted and can be cheated by bursty activities. > > The split LRU VM tries to avoid the bursty page aging as > much as possible, by doing background deactivating of > anonymous pages whenever we reclaim page cache pages and > the number of anonymous pages in the zone (or cgroup) is > low. Right, but I meant busty page allocations and accesses on them, which can make a large continuous segment of referenced pages in LRU list, say 50MB. They may or may not be valuable as a whole, however a local algorithm may keep the first 4MB and drop the remaining 46MB. Thanks, Fengguang -- 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