Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752779AbbFYPdm (ORCPT ); Thu, 25 Jun 2015 11:33:42 -0400 Received: from e18.ny.us.ibm.com ([129.33.205.208]:58327 "EHLO e18.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751555AbbFYPde (ORCPT ); Thu, 25 Jun 2015 11:33:34 -0400 X-Helo: d01dlp03.pok.ibm.com X-MailFrom: nacc@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Thu, 25 Jun 2015 08:33:28 -0700 From: Nishanth Aravamudan To: Nathan Fontenot Cc: Bharata B Rao , linuxppc-dev , "linux-kernel@vger.kernel.org" , Anton Blanchard , Paul Mackerras Subject: Re: powerpc,numa: Memory hotplug to memory-less nodes ? Message-ID: <20150625153328.GA5319@linux.vnet.ibm.com> References: <558A9EF0.3010305@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <558A9EF0.3010305@linux.vnet.ibm.com> X-Operating-System: Linux 3.13.0-40-generic (x86_64) User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15062515-0045-0000-0000-0000008B4AFE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1488 Lines: 33 On 24.06.2015 [07:13:36 -0500], Nathan Fontenot wrote: > On 06/23/2015 11:01 PM, Bharata B Rao wrote: > > So will it be correct to say that memory hotplug to memory-less node > > isn't supported by PowerPC kernel ? Should I enforce the same in QEMU > > for PowerKVM ? > > > > I'm not sure if that is correct. It appears that we initialize all online > nodes, even those without spanned_pages, at boot time. This occurs > in setup_node_data() called from initmem_init(). > > Looking at this I would think that we could add memory to any online node > even if it does not have any spanned_pages. I think an interesting test > we be to check for the node being online instead of checking to see if > it has any memory. I see no *technical* reason we should't be able to hotplug to an initially memoryless node. I'm not sure it happens in practice under PowerVM (where we have far less control of the topology anyways). One aspect of this that I have on my todo list is seeing what SLUB does when a node goes from memoryless to populated -- as during boot memoryless nodes get a 'useless' per node structure (early_kmem_cache_node_alloc). I can look at this a bit under KVM maybe later this week myself to see what happens in a guest. -Nish -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/