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    SubjectRe: [RFC] oom-kill: give the dying task a higher priority
    On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote:
    > On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
    > | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
    > | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
    > ...
    > | > | As far as my observation, RT-function always have some syscall. because pure
    > | > | calculation doesn't need deterministic guarantee. But _if_ you are really
    > | > | using such priority design. I'm ok maximum NonRT priority instead maximum
    > | > | RT priority too.
    > | >
    > | > I confess I failed to distinguish memcg OOM and system OOM and used "in
    > | > case of OOM kill the selected task the faster you can" as the guideline.
    > | > If the exit code path is short that shouldn't be a problem.
    > | >
    > | > Maybe the right way to go would be giving the dying task the biggest
    > | > priority inside that memcg to be sure that it will be the next process from
    > | > that memcg to be scheduled. Would that be reasonable?
    > |
    > | Hmm. I can't understand your point.
    > | What do you mean failing distinguish memcg and system OOM?
    > |
    > | We already have been distinguish it by mem_cgroup_out_of_memory.
    > | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR).
    > | So task selected in select_bad_process is one out of memcg's tasks when
    > | memcg have a memory pressure.
    > The approach of giving the highest priority to the dying task makes sense
    > in a system wide OOM situation. I though that would also be good for the
    > memcg OOM case.
    > After Balbir Singh's comment, I understand that in a memcg OOM the dying
    > task should have a priority just above the priority of the main task of
    > that memcg, in order to avoid interfering in the rest of the system.
    > That is the point where I failed to distinguish between memcg and system OOM.
    > Should I pursue that new idea of looking for the right priority inside the
    > memcg or is it overkill? I really don't have a clear view of the impact of
    > a memcg OOM on system performance - don't know if it is better to solve the
    > issue sooner (highest RT priority) or leave it to be solved later (highest
    > prio on the memcg). I have the impression the general case points to the
    > simpler solution.

    I think highest RT proirity ins't good solution.
    As I mentiond, Some RT functions don't want to be preempted by other processes
    which cause memory pressure. It makes RT task broken.

    On the other hand, normal processes don't have a requirement of RT.
    But it isn't a big problem that it lost little time slice, I think.
    So how about raising max normal priority?
    but I am not sure this is right solution.
    Let's listen other's opinion.
    I believe Peter have a good idea.

    > Luis
    > --
    > [ Luis Claudio R. Goncalves Bass - Gospel - RT ]
    > [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9 2696 7203 D980 A448 C8F8 ]

    Kind regards,
    Minchan Kim

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