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 C5ECF6B005A for ; Wed, 12 Aug 2009 10:32:15 -0400 (EDT) Message-ID: <4A82D24D.6020402@redhat.com> Date: Wed, 12 Aug 2009 10:31:41 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [RFC] respect the referenced bit of KVM guest pages? References: <20090806100824.GO23385@random.random> <4A7AD5DF.7090801@redhat.com> <20090807121443.5BE5.A69D9226@jp.fujitsu.com> <20090812074820.GA29631@localhost> In-Reply-To: <20090812074820.GA29631@localhost> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: KOSAKI Motohiro , Andrea Arcangeli , "Dike, Jeffrey G" , "Yu, Wilfred" , "Kleen, Andi" , Avi Kivity , Hugh Dickins , Andrew Morton , Christoph Lameter , Mel Gorman , LKML , linux-mm List-ID: Wu Fengguang wrote: > On Fri, Aug 07, 2009 at 11:17:22AM +0800, KOSAKI Motohiro wrote: >>> Andrea Arcangeli wrote: >>> >>>> Likely we need a cut-off point, if we detect it takes more than X >>>> seconds to scan the whole active list, we start ignoring young bits, >>> We could just make this depend on the calculated inactive_ratio, >>> which depends on the size of the list. >>> >>> For small systems, it may make sense to make every accessed bit >>> count, because the working set will often approach the size of >>> memory. >>> >>> On very large systems, the working set may also approach the >>> size of memory, but the inactive list only contains a small >>> percentage of the pages, so there is enough space for everything. >>> >>> Say, if the inactive_ratio is 3 or less, make the accessed bit >>> on the active lists count. >> Sound reasonable. > > Yes, such kind of global measurements would be much better. > >> How do we confirm the idea correctness? > > In general the active list tends to grow large on under-scanned LRU. > I guess Rik is pretty familiar with typical inactive_ratio values of > the large memory systems and may even have some real numbers :) > >> Wu, your X focus switching benchmark is sufficient test? > > It is a major test case for memory tight desktop. Jeff presents > another interesting one for KVM, hehe. > > Anyway I collected the active/inactive list sizes, and the numbers > show that the inactive_ratio is roughly 1 when the LRU is scanned > actively and may go very high when it is under-scanned. inactive_ratio is based on the zone (or cgroup) size. For zones it is a fixed value, which is available in /proc/zoneinfo -- All rights reversed. -- 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