From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx104.postini.com [74.125.245.104]) by kanga.kvack.org (Postfix) with SMTP id 61F716B0044 for ; Thu, 22 Mar 2012 14:48:44 -0400 (EDT) Message-ID: <4F6B73AD.5050107@redhat.com> Date: Thu, 22 Mar 2012 14:47:09 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node References: <4F6B6BFF.1020701@redhat.com> <4F6B7358.60800@gmail.com> In-Reply-To: <4F6B7358.60800@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: KOSAKI Motohiro Cc: lwoodman@redhat.com, Christoph Lameter , linux-mm@kvack.org, Linux Kernel Mailing List , Andrew Morton , Motohiro Kosaki On 03/22/2012 02:45 PM, KOSAKI Motohiro wrote: > CC to Christoph. > >> While moving tasks between cpusets I noticed some strange behavior. >> Specifically if the nodes of the destination >> cpuset are a subset of the nodes of the source cpuset >> do_migrate_pages() will move pages that are already on a node >> in the destination cpuset. The reason for this is do_migrate_pages() >> does not check whether each node in the source >> nodemask is in the destination nodemask before calling >> migrate_to_node(). If we simply do this check and skip them >> when the source is in the destination moving we wont move nodes that >> dont need to be moved. >> >> Adding a little debug printk to migrate_to_node(): >> >> Without this change migrating tasks from a cpuset containing nodes 0-7 >> to a cpuset containing nodes 3-4, we migrate >> from ALL the nodes even if they are in the both the source and >> destination nodesets: >> >> Migrating 7 to 4 >> Migrating 6 to 3 >> Migrating 5 to 4 >> Migrating 4 to 3 >> Migrating 1 to 4 >> Migrating 3 to 4 >> Migrating 0 to 3 >> Migrating 2 to 3 > > Wait. > > This may be non-optimal for cpusets, but maybe optimal migrate_pages, > especially > the usecase is HPC. I guess this is intended behavior. I think we need > to hear > Christoph's intention. How is the moving of pages that are already in the intended cpuset better than just leaving them alone? > But, I'm not against this if he has no objection. Sure. Christoph? -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org