Messages in this thread |  | | | Date | Thu, 22 Mar 2012 14:47:09 -0400 | | From | Rik van Riel <> | | Subject | Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node |
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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?
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