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    Subjectoom_kill.c badness() correction for shared memory
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    In oom_kill.c, badness() takes into account many factors, including half
    the total_vm of all the children.

    The problem with this calculation is that, if the parent and children
    share memory, the shared memory segment is counted many times for the
    parent.

    I don't think we need to count the shared memory at all when calculating
    badness, because there's already a hard limit on the amount of shared
    memory, so it's unlikely that process is runaway due to shared memory
    consumption.

    Would it be better to just use (total_vm-shared_vm) in the badness
    function in each instance it currently uses total_vm? At a minimum, we
    should do that for the loop that counts each child's vm against the
    parent.

    An example of a practical problem is with PostgreSQL. PostgreSQL
    installations often have very large shared memory regions shared between
    the parent and all the child processes. If the OOM killer is invoked,
    it's almost guaranteed to kill the PostgreSQL parent process first, even
    if the PostgreSQL processes all combined use much less memory than the
    "real" bad process (because the same shared memory is counted many
    times).

    Regards,
    Jeff Davis

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