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    Subject[PATCH -mm V2] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node
    While moving tasks between cpusets we 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

    This version of the patch will only skips migrating from nodes that are
    not in the destination
    nodesets if the number of nodes in the source and destination nodesets
    are not equal. This
    preserves the intended behavior that Christoph pointed out yet aviods
    the costly overhead
    of migrating them when its not necessary.


    Here is timings of migrating from nodes 0-7 to 1 & 3 with and without
    the patch:

    BEFORE PATCH -- Move times: 59, 140, 651 seconds
    ============

    Moving 14 tasks from nodes (0-7) to nodes (1,3)
    numad(8780) do_migrate_pages (mm=0xffff88081d414400
    from_nodes=0xffff880818c81d28 to_nodes=0xffff880818c81ce8 flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x7 dest=0x3
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x6 dest=0x1
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x5 dest=0x3
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x4 dest=0x1
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x2 dest=0x1
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x1 dest=0x3
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d414400 source=0x0 dest=0x1
    flags=0x4)
    (Above moves repeated for each of the 14 tasks...)
    PID 8890 moved to node(s) 1,3 in 59.2 seconds


    Moving 20 tasks from nodes (0-7) to nodes (1,4-5)
    numad(8780) do_migrate_pages (mm=0xffff88081d88c700
    from_nodes=0xffff880818c81d28 to_nodes=0xffff880818c81ce8 flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d88c700 source=0x7 dest=0x4
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d88c700 source=0x6 dest=0x1
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d88c700 source=0x3 dest=0x1
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d88c700 source=0x2 dest=0x5
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d88c700 source=0x1 dest=0x4
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d88c700 source=0x0 dest=0x1
    flags=0x4)
    (Above moves repeated for each of the 20 tasks...)
    PID 8962 moved to node(s) 1,4-5 in 139.88 seconds


    Moving 26 tasks from nodes (0-7) to nodes (1-3,5)
    numad(8780) do_migrate_pages (mm=0xffff88081d5bc740
    from_nodes=0xffff880818c81d28 to_nodes=0xffff880818c81ce8 flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x7 dest=0x5
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x6 dest=0x3
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x5 dest=0x2
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x3 dest=0x5
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x2 dest=0x3
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x1 dest=0x2
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x0 dest=0x1
    flags=0x4)
    numad(8780) migrate_to_node (mm=0xffff88081d5bc740 source=0x4 dest=0x1
    flags=0x4)
    (Above moves repeated for each of the 26 tasks...)
    PID 9058 moved to node(s) 1-3,5 in 651.45 seconds



    AFTER PATCH -- Move times: 42, 56, 93 seconds
    ===========

    Moving 14 tasks from nodes (0-7) to nodes (5,7)
    numad(33209) do_migrate_pages (mm=0xffff88101d5ff140
    from_nodes=0xffff88101e7b5d28 to_nodes=0xffff88101e7b5ce8 flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d5ff140 source=0x6 dest=0x5
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d5ff140 source=0x4 dest=0x5
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d5ff140 source=0x3 dest=0x7
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d5ff140 source=0x2 dest=0x5
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d5ff140 source=0x1 dest=0x7
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d5ff140 source=0x0 dest=0x5
    flags=0x4)
    (Above moves repeated for each of the 14 tasks...)
    PID 33221 moved to node(s) 5,7 in 41.67 seconds


    Moving 20 tasks from nodes (0-7) to nodes (1,3,5)
    numad(33209) do_migrate_pages (mm=0xffff88101d6c37c0
    from_nodes=0xffff88101e7b5d28 to_nodes=0xffff88101e7b5ce8 flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d6c37c0 source=0x7 dest=0x3
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d6c37c0 source=0x6 dest=0x1
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d6c37c0 source=0x4 dest=0x3
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d6c37c0 source=0x2 dest=0x5
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d6c37c0 source=0x0 dest=0x1
    flags=0x4)
    (Above moves repeated for each of the 20 tasks...)
    PID 33289 moved to node(s) 1,3,5 in 56.3 seconds


    Moving 26 tasks from nodes (0-7) to nodes (1,3,5,7)
    numad(33209) do_migrate_pages (mm=0xffff88101d924400
    from_nodes=0xffff88101e7b5d28 to_nodes=0xffff88101e7b5ce8 flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d924400 source=0x6 dest=0x5
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d924400 source=0x4 dest=0x1
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d924400 source=0x2 dest=0x5
    flags=0x4)
    numad(33209) migrate_to_node (mm=0xffff88101d924400 source=0x0 dest=0x1
    flags=0x4)
    (Above moves repeated for each of the 26 tasks...)
    PID 33372 moved to node(s) 1,3,5,7 in 92.67 seconds


    Signed-off-by: Larry Woodman<lwoodman@redhat.com>


    diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    index 47296fe..6c189fa 100644
    --- a/mm/mempolicy.c
    +++ b/mm/mempolicy.c
    @@ -1012,6 +1012,16 @@ int do_migrate_pages(struct mm_struct *mm,
    int dest = 0;

    for_each_node_mask(s, tmp) {
    +
    + /* IFF there is an equal number of source and
    + * destination nodes, maintain relative node distance
    + * even when source and destination nodes overlap.
    + * However, when the node weight is unequal, never move
    + * memory out of any destination nodes */
    + if ((nodes_weight(*from_nodes) != nodes_weight(*to_nodes)) &&
    + (node_isset(s, *to_nodes)))
    + continue;
    +
    d = node_remap(s, *from_nodes, *to_nodes);
    if (s == d)
    continue;
    \
     
     \ /
      Last update: 2012-04-24 18:07    [W:0.043 / U:90.744 seconds]
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