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@xxxxxxxxxx>
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