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    SubjectRe: [PATCH 9/9] oom: give the dying task a higher priority
    On Wed, Jun 16, 2010 at 08:36:29PM +0900, KOSAKI Motohiro wrote:
    >
    > From: Luis Claudio R. Goncalves <lclaudio@uudg.org>
    >
    > In a system under heavy load it was observed that even after the
    > oom-killer selects a task to die, the task may take a long time to die.
    >
    > Right after sending a SIGKILL to the task selected by the oom-killer
    > this task has it's priority increased so that it can exit() exit soon,
    > freeing memory. That is accomplished by:
    >
    > /*
    > * We give our sacrificial lamb high priority and access to
    > * all the memory it needs. That way it should be able to
    > * exit() and clear out its resources quickly...
    > */
    > p->rt.time_slice = HZ;
    > set_tsk_thread_flag(p, TIF_MEMDIE);
    >
    > It sounds plausible giving the dying task an even higher priority to be
    > sure it will be scheduled sooner and free the desired memory. It was
    > suggested on LKML using SCHED_FIFO:1, the lowest RT priority so that
    > this task won't interfere with any running RT task.
    >
    > If the dying task is already an RT task, leave it untouched.
    > Another good suggestion, implemented here, was to avoid boosting the
    > dying task priority in case of mem_cgroup OOM.
    >
    > Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>
    > Cc: Minchan Kim <minchan.kim@gmail.com>
    > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > ---
    > mm/oom_kill.c | 38 +++++++++++++++++++++++++++++++++++---
    > 1 files changed, 35 insertions(+), 3 deletions(-)
    >
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index 7e9942d..1ecfc7a 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -82,6 +82,28 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk,
    > #endif /* CONFIG_NUMA */
    >
    > /*
    > + * If this is a system OOM (not a memcg OOM) and the task selected to be
    > + * killed is not already running at high (RT) priorities, speed up the
    > + * recovery by boosting the dying task to the lowest FIFO priority.
    > + * That helps with the recovery and avoids interfering with RT tasks.
    > + */
    > +static void boost_dying_task_prio(struct task_struct *p,
    > + struct mem_cgroup *mem)
    > +{
    > + struct sched_param param = { .sched_priority = 1 };
    > +
    > + if (mem)
    > + return;
    > +
    > + if (rt_task(p)) {
    > + p->rt.time_slice = HZ;
    > + return;

    I have a question from long time ago.
    If we change rt.time_slice _without_ setscheduler, is it effective?
    I mean scheduler pick up the task faster than other normal task?

    > + }
    > +
    > + sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
    > +}
    > +
    > +/*
    --
    Kind regards,
    Minchan Kim


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