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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