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    SubjectRe: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic
    On Mon, 27 Jul 2009 10:55:47 -0700 (PDT)
    David Rientjes <rientjes@google.com> wrote:

    > On Sat, 25 Jul 2009, KAMEZAWA Hiroyuki wrote:
    >
    > > _Direct_ use of task->mems_allowed is only in cpuset and mempolicy.
    > > If no policy is used, it's not checked.
    > > (See alloc_pages_current())
    > >
    > > memory hotplug's notifier just updates top_cpuset's mems_allowed.
    > > But it doesn't update each task's ones.
    >
    > That's not true, cpuset_track_online_nodes() will call
    > scan_for_empty_cpusets() on top_cpuset, which works from the root to
    > leaves updating each cpuset's mems_allowed by intersecting it with
    > node_states[N_HIGH_MEMORY]. This is done as part of the MEM_OFFLINE
    > callback in the cpuset code, so N_HIGH_MEMORY represents the nodes still
    > online.
    >
    yes.

    > The nodemask for each task is updated to reflect the removal of a node and
    > it calls mpol_rebind_mm() with the new nodemask.
    >
    yes, but _not_ updated at online.

    > This is admittedly pretty late to be removing mems from cpusets (and
    > mempolicies) when the unplug has already happened. We should look at
    > doing the rebind for MEM_GOING_OFFLINE.
    >
    Hm.

    What I felt at reading cpuset/mempolicy again is that it's too complex ;)
    The 1st question is why mems_allowed which can be 1024bytes when max_node=4096
    is copied per tasks....
    And mempolicy code uses too much nodemask_t on stack.

    I'll try some, today, including this bug-fix.

    Thanks,
    -Kame








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