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    SubjectRe: [BUGFIX][PATCH] oom-kill: fix NUMA consraint check with nodemask v4.2
    On Tue, 15 Dec 2009, KOSAKI Motohiro wrote:

    > > A few requirements that I have:
    >
    > Um, good analysis! really.
    >
    > >
    > > - we must be able to define when a task is a memory hogger; this is
    > > currently done by /proc/pid/oom_adj relying on the overall total_vm
    > > size of the task as a baseline. Most users should have a good sense
    > > of when their task is using more memory than expected and killing a
    > > memory leaker should always be the optimal oom killer result. A better
    > > set of units other than a shift on total_vm would be helpful, though.
    >
    > nit: What's mean "Most users"? desktop user(one of most majority users)
    > don't have any expection of memory usage.
    >
    > but, if admin have memory expection, they should be able to tune
    > optimal oom result.
    >
    > I think you pointed right thing.
    >

    This is mostly referring to production server users where memory
    consumption by particular applications can be estimated, which allows the
    kernel to determine when a task is using a wildly unexpected amount that
    happens to become egregious enough to force the oom killer into killing a
    task.

    That is contrast to using rss as a baseline where we prefer on killing the
    application with the most resident RAM. It is not always ideal to kill a
    task with 8GB of rss when we fail to allocate a single page for a low
    priority task.

    > > - we must prefer tasks that run on a cpuset or mempolicy's nodes if the
    > > oom condition is constrained by that cpuset or mempolicy and its not a
    > > system-wide issue.
    >
    > agreed. (who disagree it?)
    >

    It's possible to nullify the current penalization in the badness heuristic
    (order 3 reduction) if a candidate task does not share nodes with
    current's allowed set either by way of cpusets or mempolicies. For
    example, an oom caused by an application with an MPOL_BIND on a single
    node can easily kill a task that has no memory resident on that node if
    its usage (or rss) is 3 orders higher than any candidate that is allowed
    on my bound node.

    > > - we must be able to polarize the badness heuristic to always select a
    > > particular task is if its very low priority or disable oom killing for
    > > a task if its must-run.
    >
    > Probably I haven't catch your point. What's mean "polarize"? Can you
    > please describe more?
    >

    We need to be able to polarize tasks so they are always killed regardless
    of any kernel heuristic (/proc/pid/oom_adj of +15, currently) or always
    chosen last (-16, currently). We also need a way of completely disabling
    oom killing for certain tasks such as with OOM_DISABLE.


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