Messages in this thread Patch in this message | | | Date | Thu, 22 Mar 2012 14:14:23 -0400 | From | Larry Woodman <> | Subject | [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node |
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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
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>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 47296fe..2bd13e9 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1012,6 +1012,9 @@ int do_migrate_pages(struct mm_struct *mm, int dest = 0; for_each_node_mask(s, tmp) { + /* no need to move if its already there */ + if (node_isset(s, *to_nodes)) + continue; d = node_remap(s, *from_nodes, *to_nodes); if (s == d) continue; | |