Messages in this thread | | | Date | Thu, 22 Mar 2012 14:45:44 -0400 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node |
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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.
But, I'm not against this if he has no objection.
> > > With this change we only migrate from nodes that are not in the destination nodesets: > > Migrating 7 to 4 > Migrating 6 to 3 > Migrating 5 to 4 > Migrating 2 to 3 > Migrating 1 to 4 > Migrating 0 to 3 > > Signed-off-by: Larry Woodman<lwoodman@redhat.com> >
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