From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH] [RESEND] x86_64: add memory hotremove config option Date: Mon, 8 Sep 2008 15:52:49 +1000 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: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen 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 List-ID: 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. -- 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