Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754581AbZIIX6V (ORCPT ); Wed, 9 Sep 2009 19:58:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752642AbZIIX6V (ORCPT ); Wed, 9 Sep 2009 19:58:21 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:38749 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752751AbZIIX6U convert rfc822-to-8bit (ORCPT ); Wed, 9 Sep 2009 19:58:20 -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: <28c262360909090839j626ff818of930cf13a6185123@mail.gmail.com> References: <20090909131945.0CF5.A69D9226@jp.fujitsu.com> <28c262360909090839j626ff818of930cf13a6185123@mail.gmail.com> Message-Id: <20090910084602.9CBD.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8BIT X-Mailer: Becky! ver. 2.50.07 [ja] Date: Thu, 10 Sep 2009 08:58:20 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2220 Lines: 52 > 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... ;) 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. -- 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/