From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753417AbYIHFxW (ORCPT ); Mon, 8 Sep 2008 01:53:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752501AbYIHFxN (ORCPT ); Mon, 8 Sep 2008 01:53:13 -0400 Received: from smtp101.mail.mud.yahoo.com ([209.191.85.211]:24847 "HELO smtp101.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752497AbYIHFxM (ORCPT ); Mon, 8 Sep 2008 01:53:12 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:X-Yahoo-Newman-Property:From:To:Subject:Date:User-Agent:Cc:References:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-Disposition:Message-Id; b=NhaSceNqDnvxoipvyqAdEuGpRUDVK0qDDdFFPmTh9KcaRGLhhHo6KvECbAuw8V4UI5NxIW4eu0krr6NU6+42jBimpeX5lLm+0Z/iB3wcaCrsN/d7augYZP+A0J2Ik+Jwa8sS0PBYIDKNwrO3qgw7/1lkFyXwYqvKRPNTYLdXoO4= ; X-YMail-OSG: tB0Xg6cVM1mIeYsyLX8WNqXqDw5ucxV3Hq8q7da6ghETTp08zRjgw4S_9Jl5gAyfk.phl5kJa349hSTSas4Y1DqewR2RKySiM3xxIWjDYMKTfsCSiOqfNf3xdGCDDFcrZxs- X-Yahoo-Newman-Property: ymail-3 From: Nick Piggin To: Andi Kleen Subject: Re: [PATCH] [RESEND] x86_64: add memory hotremove config option Date: Mon, 8 Sep 2008 15:52:49 +1000 User-Agent: KMail/1.9.5 Cc: Yasunori Goto , Gary Hade , linux-mm@kvack.org, Andrew Morton , Badari Pulavarty , Mel Gorman , Chris McDermott , linux-kernel@vger.kernel.org, x86@kernel.org, Ingo Molnar References: <20080905215452.GF11692@us.ibm.com> <20080906153855.7260.E1E9C6FF@jp.fujitsu.com> <20080906085320.GE18288@one.firstfloor.org> In-Reply-To: <20080906085320.GE18288@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200809081552.50126.nickpiggin@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 06 September 2008 18:53, Andi Kleen wrote: > On Sat, Sep 06, 2008 at 04:06:38PM +0900, Yasunori Goto wrote: > > > not. > > > > > > This means I don't see a real use case for this feature. > > > > I don't think its driver is almighty. > > IIRC, balloon driver can be cause of fragmentation for 24-7 system. > > Sure the balloon driver can be likely improved too, it's just > that I don't think a balloon driver should call into the function > the original patch in the series hooked up. > > > In addition, I have heard that memory hotplug would be useful for > > reducing of power consumption of DIMM. > > It's unclear that memory hotplug is the right model for DIMM power > management. The problem is that DIMMs are interleaved, so you again have to > completely free a quite large area. It's not much easier than node hotplug. > > > I have to admit that memory hotplug has many issues, but I would like to > > Let's call it "node" or "hardware" memory hot unplug, not that > anyone confuses it with the easier VM based hot unplug or the really > easy hotadd. > > > solve them step by step. > > The question is if they are even solvable in a useful way. > I'm not sure it's that useful to start and then find out > that it doesn't work anyways. You use non-linear mappings for the kernel, so that kernel data is not tied to a specific physical address. AFAIK, that is the only way to really do it completely (like the fragmentation problem). Of course, I don't think that would be a good idea to do that in the forseeable future.