From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 11 Apr 2006 14:03:31 -0500 From: Jack Steiner Subject: Re: [PATCH 2.6.17-rc1-mm1 0/6] Migrate-on-fault - Overview Message-ID: <20060411190330.GA21229@sgi.com> References: <1144441108.5198.36.camel@localhost.localdomain> <200604112052.50133.ak@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200604112052.50133.ak@suse.de> Sender: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen Cc: Christoph Lameter , Lee Schermerhorn , linux-mm , ak@suse.com List-ID: On Tue, Apr 11, 2006 at 08:52:49PM +0200, Andi Kleen wrote: > On Tuesday 11 April 2006 20:46, Christoph Lameter wrote: > > However, if the page is not frequently references then the > > effort required to migrate the page was not justified. > > I have my doubts the whole thing is really worthwhile. It probably > would at least need some statistics to only do this for frequent > accesses, but I don't know where to put this data. Agree. And a way to disable the migration-on-fault. > > At least it would be a serious research project to figure out > a good way to do automatic migration. From what I was told by > people who tried this (e.g. in Irix) it is really hard and > didn't turn out to be a win for them. IRIX had hardware support for counting offnode vs. onnode references to a page & sending interrupts when migration appeared to be beneficial We intended to use this info to migrate pages. Unfortunately, we were never able to demonstrate a performance benefit of migrating pages. The overhead always exceeded the cost except in a very small number of carefully selected benchmarks. > > The better way is to just provide the infrastructure > and let batch managers or program itselves take care of migration. > > That was the whole idea behind NUMA API - some problems > are too hard to figure out automatically by the kernel, so > allow the user or application to give it a hand. > > And frankly the defaults we have currently are not that bad, > perhaps with some small tweaks (e.g. i'm still liking the idea > of interleaving file cache by default) > > -Andi > -- Jack -- 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