From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Date: Fri, 11 Jul 2014 20:02:14 +0000 Subject: Re: [RFC Patch V1 00/30] Enable memoryless node on x86 platforms Message-Id: <53C042C6.2020507@intel.com> List-Id: References: <1405064267-11678-1-git-send-email-jiang.liu@linux.intel.com> <20140711082956.GC20603@laptop.programming.kicks-ass.net> <20140711153314.GA6155@kroah.com> In-Reply-To: <20140711153314.GA6155@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Greg KH , Jiang Liu Cc: Peter Zijlstra , Andrew Morton , Mel Gorman , David Rientjes , Mike Galbraith , "Rafael J . Wysocki" , Tony Luck , linux-mm@kvack.org, linux-hotplug@vger.kernel.org, linux-kernel@vger.kernel.org On 07/11/2014 08:33 AM, Greg KH wrote: > On Fri, Jul 11, 2014 at 10:29:56AM +0200, Peter Zijlstra wrote: >> > On Fri, Jul 11, 2014 at 03:37:17PM +0800, Jiang Liu wrote: >>> > > Any comments are welcomed! >> > >> > Why would anybody _ever_ have a memoryless node? That's ridiculous. > I'm with Peter here, why would this be a situation that we should even > support? Are there machines out there shipping like this? This is orthogonal to the problem Jiang Liu is solving, but... The IBM guys have been hitting the CPU-less and memoryless node issues forever, but that's mostly because their (traditional) hypervisor had good NUMA support and ran multi-node guests. I've never seen it in practice on x86 mostly because the hypervisors don't have good NUMA support. I honestly think this is something x86 is going to have to handle eventually anyway. It's essentially a resource fragmentation problem, and there are going to be times where a guest needs to be spun up and hypervisor has nodes with either no spare memory or no spare CPUs. The hypervisor has 3 choices in this case: 1. Lie about the NUMA layout 2. Waste the resources 3. Tell the guest how it's actually arranged