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    SubjectRe: [RFC] oom-kill: give the dying task a higher priority
    On Fri, May 28, 2010 at 01:48:26PM -0300, Luis Claudio R. Goncalves wrote:
    > On Sat, May 29, 2010 at 12:45:49AM +0900, Minchan Kim wrote:
    > | On Fri, May 28, 2010 at 12:28:42PM -0300, Luis Claudio R. Goncalves wrote:
    > | > On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
    > ...
    > | > | 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.
    > | >
    > | > For the RT case, if you reached a system OOM situation, your determinism has
    > | > already been hurt. If the memcg OOM happens on the same memcg your RT task
    > | > is - what will probably be the case most of time - again, the determinism
    > | > has deteriorated. For both these cases, giving the dying task SCHED_FIFO
    > | > MAX_RT_PRIO-1 means a faster recovery.
    > |
    > | What I want to say is that determinisic has no relation with OOM.
    > | Why is some RT task affected by other process's OOM?
    > |
    > | Of course, if system has no memory, it is likely to slow down RT task.
    > | But it's just only thought. If some task scheduled just is exit, we don't need
    > | to raise OOMed task's priority.
    > |
    > | But raising min rt priority on your patch was what I want.
    > | It doesn't preempt any RT task.
    > |
    > | So until now, I have made noise about your patch.
    > | Really, sorry for that.
    > | I don't have any objection on raising priority part from now on.
    >
    > This is the third version of the patch, factoring in your input along with
    > Peter's comment. Basically the same patch, but using the lowest RT priority
    > to boost the dying task.
    >
    > Thanks again for reviewing and commenting.
    > Luis
    >
    > oom-killer: give the dying task rt priority (v3)
    >
    > Give the dying task RT priority so that it can be scheduled quickly and die,
    > freeing needed memory.
    >
    > Signed-off-by: Luis Claudio R. Gonçalves <lgoncalv@redhat.com>
    >
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index 84bbba2..2b0204f 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -266,6 +266,8 @@ static struct task_struct *select_bad_process(unsigned long *ppoints)
    > */
    > static void __oom_kill_task(struct task_struct *p, int verbose)
    > {
    > + struct sched_param param;
    > +
    > if (is_global_init(p)) {
    > WARN_ON(1);
    > printk(KERN_WARNING "tried to kill init!\n");
    > @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
    > * exit() and clear out its resources quickly...
    > */
    > p->time_slice = HZ;
    > + param.sched_priority = MAX_RT_PRIO-10;

    I can't understand your point, still.
    Why you put the priority as "MAX_RT_PRIO - 10"?
    What I and peter mentioned was "1" which is lowest RT priority.

    > + sched_setscheduler(p, SCHED_FIFO, &param);

    Why do you change sched_setscheduler_nocheck with sched_set_scheduler?
    It means you can't boost prioity if current context doesn't have permission.
    Is it a your intention?

    > set_tsk_thread_flag(p, TIF_MEMDIE);
    >
    > force_sig(SIGKILL, p);
    > --
    > [ 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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