From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754365AbcKJDRf (ORCPT ); Wed, 9 Nov 2016 22:17:35 -0500 Received: from szxga02-in.huawei.com ([119.145.14.65]:55862 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753745AbcKJDRe (ORCPT ); Wed, 9 Nov 2016 22:17:34 -0500 Message-ID: <5823E6AF.8040600@huawei.com> Date: Thu, 10 Nov 2016 11:17:03 +0800 From: Xishi Qiu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Mel Gorman CC: Vlastimil Babka , Andrew Morton , Tang Chen , Linux MM , LKML , "robert.liu@huawei.com" Subject: Re: [RFC] mem-hotplug: shall we skip unmovable node when doing numa balance? References: <582157E5.8000106@huawei.com> <20161109115827.GD3614@techsingularity.net> In-Reply-To: <20161109115827.GD3614@techsingularity.net> Content-Type: text/plain; charset="ISO-8859-15" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.25.179] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/11/9 19:58, Mel Gorman wrote: > On Tue, Nov 08, 2016 at 12:43:17PM +0800, Xishi Qiu wrote: >> On mem-hotplug system, there is a problem, please see the following case. >> >> memtester xxG, the memory will be alloced on a movable node. And after numa >> balancing, the memory may be migrated to the other node, it may be a unmovable >> node. This will reduce the free memory of the unmovable node, and may be oom >> later. >> > > How would it OOM later? It's movable memmory that is moving via > automatic NUMA balancing so at the very least it can be reclaimed. If > the memory is mlocked or unable to migrate then it's irrelevant if > automatic balancing put it there. > Hi Mel, memtester will mlock the memory, so we can not reclaim, then maybe oom, right? So let the manager set some numa policies to prevent the above case, right? Thanks, Xishi Qiu >> My question is that shall we skip unmovable node when doing numa balance? >> or just let the manager set some numa policies? >> > > If the unmovable node must be protected from automatic NUMA balancing > then policies are the appropriate step to prevent the processes running > on that node or from allocating memory on that node. > > Either way, protecting unmovable nodes in the name of hotplug is pretty > much guaranteed to be a performance black hole because at the very > least, page table pages will always be remote accesses for processes > running on the unmovable node. > >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index 057964d..f0954ac 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -2334,6 +2334,13 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long >> out: >> mpol_cond_put(pol); >> >> + /* Skip unmovable nodes when do numa balancing */ >> + if (movable_node_enabled && ret != -1) { >> + zone = NODE_DATA(ret)->node_zones + MAX_NR_ZONES - 1; >> + if (!populated_zone(zone)) >> + ret = -1; >> + } >> + >> return ret; >> } > > Nak. >