From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx160.postini.com [74.125.245.160]) by kanga.kvack.org (Postfix) with SMTP id 4958A6B004A for ; Mon, 19 Mar 2012 11:45:42 -0400 (EDT) Message-ID: <4F67546A.9060803@redhat.com> Date: Mon, 19 Mar 2012 17:44:42 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [RFC][PATCH 00/26] sched/numa References: <20120316144028.036474157@chello.nl> <4F670325.7080700@redhat.com> <1332155527.18960.292.camel@twins> <4F671B90.3010209@redhat.com> <1332159657.18960.321.camel@twins> <4F67257F.4030803@redhat.com> In-Reply-To: <4F67257F.4030803@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Linus Torvalds , Andrew Morton , Thomas Gleixner , Ingo Molnar , Paul Turner , Suresh Siddha , Mike Galbraith , "Paul E. McKenney" , Lai Jiangshan , Dan Smith , Bharata B Rao , Lee Schermerhorn , Andrea Arcangeli , Rik van Riel , Johannes Weiner , linux-kernel@vger.kernel.org, linux-mm@kvack.org On 03/19/2012 02:24 PM, Avi Kivity wrote: > On 03/19/2012 02:20 PM, Peter Zijlstra wrote: > > On Mon, 2012-03-19 at 13:42 +0200, Avi Kivity wrote: > > > It's the standard space/time tradeoff. Once solution wants more > > > storage, the other wants more faults. > > > > > > Note scanners can use A/D bits which are cheaper than faults. > > > > I'm not convinced.. the scanner will still consume time even if the > > system is perfectly balanced -- it has to in order to determine this. > > > > So sure, A/D/other page table magic can make scanners faster than faults > > however you only need faults when you're actually going to migrate a > > task. Whereas you always need to scan, even in the stable state. > > > > So while the per-instance times might be in favour of scanning, I'm > > thinking the accumulated time is in favour of faults. > > When you migrate a vnode, you don't need the faults at all. You know > exactly which pages need to be migrated, you can just queue them > immediately when you make that decision. > > The scanning therefore only needs to pick up the stragglers and can be > set to a very low frequency. Running the numbers, 4GB = 1Mpages, at 2us per page migration that's 2 seconds to migrate an entire process, perhaps 2x-3x that for kvm. So as long numa balancing happens at a lower frequency than once every few minutes, the gains should be higher than the loss. If those numbers are not too wrong then migrate on fault should be a win. -- error compiling committee.c: too many arguments to function -- 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