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    SubjectRe: [PATCH v2] cpusets: randomize node rotor used in cpuset_mem_spread_node()
    On Fri, 15 Apr 2011 10:20:51 +0200
    Michal Hocko <mhocko@suse.cz> wrote:

    > Some workloads that create a large number of small files tend to assign
    > too many pages to node 0 (multi-node systems). Part of the reason is that
    > the rotor (in cpuset_mem_spread_node()) used to assign nodes starts at
    > node 0 for newly created tasks.
    >
    > This patch changes the rotor to be initialized to a random node number of
    > the cpuset. We are initializating it lazily in cpuset_mem_spread_node
    > resp. cpuset_slab_spread_node.
    >
    >
    > ...
    >
    > --- a/kernel/cpuset.c
    > +++ b/kernel/cpuset.c
    > @@ -2465,11 +2465,19 @@ static int cpuset_spread_node(int *rotor)
    >
    > int cpuset_mem_spread_node(void)
    > {
    > + if (current->cpuset_mem_spread_rotor == -1)
    > + current->cpuset_mem_spread_rotor =
    > + node_random(&current->mems_allowed);
    > +
    > return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
    > }
    >
    > int cpuset_slab_spread_node(void)
    > {
    > + if (current->cpuset_slab_spread_rotor == -1)
    > + current->cpuset_slab_spread_rotor
    > + = node_random(&current->mems_allowed);
    > +
    > return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
    > }
    >

    alpha allmodconfig:

    kernel/built-in.o: In function `cpuset_slab_spread_node':
    (.text+0x67360): undefined reference to `node_random'
    kernel/built-in.o: In function `cpuset_slab_spread_node':
    (.text+0x67368): undefined reference to `node_random'
    kernel/built-in.o: In function `cpuset_mem_spread_node':
    (.text+0x673b8): undefined reference to `node_random'
    kernel/built-in.o: In function `cpuset_mem_spread_node':
    (.text+0x673c0): undefined reference to `node_random'

    because it has CONFIG_NUMA=n, CONFIG_NODES_SHIFT=7.

    We use "#if MAX_NUMNODES > 1" in nodemask.h, but we use CONFIG_NUMA
    when deciding to build mempolicy.o. That's a bit odd - why didn't
    nodemask.h use CONFIG_NUMA?



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