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    SubjectRe: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic
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    KAMEZAWA Hiroyuki wrote:
    > KAMEZAWA Hiroyuki wrote:
    > Then, here is a much easier fix. for trusting cpuset more.
    >
    just a memo about memory hotplug

    _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.
    Then, task's bahavior is

    - tasks which don't use mempolicy will use all nodes, N_HIGH_MEMORY.
    - tasks under cpuset will be controlled under their own cpuset.
    - tasks under mempolicy will use their own policy.
    but no new policy is re-calculated and, then, no new mask.

    Now, even if all memory on nodes a removed, pgdat just remains.
    Then, cpuset/mempolicy will never access NODE_DATA(nid) which is NULL.

    Thanks,
    -Kame



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