Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753887AbZIJBPI (ORCPT ); Wed, 9 Sep 2009 21:15:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753320AbZIJBPH (ORCPT ); Wed, 9 Sep 2009 21:15:07 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:43637 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751679AbZIJBPG (ORCPT ); Wed, 9 Sep 2009 21:15:06 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Minchan Kim Subject: Re: [rfc] lru_add_drain_all() vs isolation Cc: kosaki.motohiro@jp.fujitsu.com, Christoph Lameter , Peter Zijlstra , Mike Galbraith , Ingo Molnar , linux-mm , Oleg Nesterov , lkml In-Reply-To: <20090910100057.a1375276.minchan.kim@barrios-desktop> References: <20090910084602.9CBD.A69D9226@jp.fujitsu.com> <20090910100057.a1375276.minchan.kim@barrios-desktop> Message-Id: <20090910101051.9CCC.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Thu, 10 Sep 2009 10:15:07 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3105 Lines: 76 > On Thu, 10 Sep 2009 08:58:20 +0900 (JST) > KOSAKI Motohiro wrote: > > > > On Wed, Sep 9, 2009 at 1:27 PM, KOSAKI Motohiro > > > wrote: > > > >> The usefulness of a scheme like this requires: > > > >> > > > >> 1. There are cpus that continually execute user space code > > > >>    without system interaction. > > > >> > > > >> 2. There are repeated VM activities that require page isolation / > > > >>    migration. > > > >> > > > >> The first page isolation activity will then clear the lru caches of the > > > >> processes doing number crunching in user space (and therefore the first > > > >> isolation will still interrupt). The second and following isolation will > > > >> then no longer interrupt the processes. > > > >> > > > >> 2. is rare. So the question is if the additional code in the LRU handling > > > >> can be justified. If lru handling is not time sensitive then yes. > > > > > > > > Christoph, I'd like to discuss a bit related (and almost unrelated) thing. > > > > I think page migration don't need lru_add_drain_all() as synchronous, because > > > > page migration have 10 times retry. > > > > > > > > Then asynchronous lru_add_drain_all() cause > > > > > > > >  - if system isn't under heavy pressure, retry succussfull. > > > >  - if system is under heavy pressure or RT-thread work busy busy loop, retry failure. > > > > > > > > I don't think this is problematic bahavior. Also, mlock can use asynchrounous lru drain. > > > > > > I think, more exactly, we don't have to drain lru pages for mlocking. > > > Mlocked pages will go into unevictable lru due to > > > try_to_unmap when shrink of lru happens. > > > > Right. > > > > > How about removing draining in case of mlock? > > > > Umm, I don't like this. because perfectly no drain often make strange test result. > > I mean /proc/meminfo::Mlock might be displayed unexpected value. it is not leak. it's only lazy cull. > > but many tester and administrator wiill think it's bug... ;) > > I agree. I have no objection to your approach. :) > > > Practically, lru_add_drain_all() is nearly zero cost. because mlock's page fault is very > > costly operation. it hide drain cost. now, we only want to treat corner case issue. > > I don't hope dramatic change. > > Another problem is as follow. > > Although some CPUs don't have any thing to do, we do it. > HPC guys don't want to consume CPU cycle as Christoph pointed out. > I liked Peter's idea with regard to this. > My approach can solve it, too. > But I agree it would be dramatic change. Is Perter's + mine approach bad? It mean, - RT-thread binding cpu is not grabbing the page -> mlock successful by Peter's improvement - RT-thread binding cpu is grabbing the page -> mlock successful by mine approach the page is culled later. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/