From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH/RFC 0/8] numa - Migrate-on-Fault Date: Mon, 15 Nov 2010 15:21:22 +0100 Message-ID: <20101115142122.GK7269@basil.fritz.box> References: <20101111194450.12535.12611.sendpatchset@zaphod.localdomain> <20101114152440.E02E.A69D9226@jp.fujitsu.com> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-numa-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Christoph Lameter Cc: KOSAKI Motohiro , Lee Schermerhorn , linux-numa@vger.kernel.org, akpm@linux-foundation.org, Mel Gorman , Nick Piggin , Hugh Dickins , andi@firstfloor.org, David Rientjes , Avi Kivity , Andrea Arcangeli , linux-mm@kvack.org [Adding linux-mm where this should have been in the first place] On Mon, Nov 15, 2010 at 08:13:14AM -0600, Christoph Lameter wrote: > On Sun, 14 Nov 2010, KOSAKI Motohiro wrote: > > > Nice! > > Lets not get overenthused. There has been no conclusive proof that the > overhead introduced by automatic migration schemes is consistently less > than the benefit obtained by moving the data. Quite to the contrary. We > have over a decades worth of research and attempts on this issue and there > was no general improvement to be had that way. I agree it's not a good idea to enable this by default because the cost of doing it wrong is too severe. But I suspect it's a good idea to have optionally available for various workloads. Good candidates so far: - Virtualization with KVM (I think it's very promising for that) Basically this allows to keep guests local on nodes with their own NUMA policy without having to statically bind them. - Some HPC workloads. There were various older reports that it helped there. So basically I think automatic migration would be good to have as another option to enable in numactl. -Andi -- ak@linux.intel.com -- Speaking for myself only.