From mboxrd@z Thu Jan 1 00:00:00 1970 From: KOSAKI Motohiro Subject: Re: [PATCH/RFC 0/8] numa - Migrate-on-Fault Date: Tue, 16 Nov 2010 13:54:01 +0900 (JST) Message-ID: <20101116134644.BF21.A69D9226@jp.fujitsu.com> References: <20101114152440.E02E.A69D9226@jp.fujitsu.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-numa-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Christoph Lameter Cc: kosaki.motohiro@jp.fujitsu.com, 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 > 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. > > The reason that the manual placement interfaces exist is because there was > no generally beneficial migration scheme available. The manual interfaces > allow the writing of various automatic migrations schemes in user space. > > If wecan come up with something that is an improvement then lets go > this way but I am skeptical. Ah, I thought this series only has manua migration (i.e. MPOL_MF_LAZY), but it also has automatic migration if a page is not mapped. So my standpoint is, manual lazy migration has certinally usecase. but I have no opinion against automatic one.