Re: [PATCH 10/11] oom: give the dying task a higher priority

[Minchan Kim <minchan.kim@gmail.com>]

On Wed, Jun 30, 2010 at 06:35:08PM +0900, KOSAKI Motohiro wrote:
> 
> Sorry, I forgot to cc Luis. resend.
> 
> 
> (intentional full quote)
> 
> > 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>

Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

It seems code itself doesn't have a problem.
So I give reviewed-by.
But this patch might break fairness of normal process at corner case.
If system working is more important than fairness of processes,
It does make sense. But scheduler guys might have a different opinion.

So at least, we need ACKs of scheduler guys.
Cced Ingo, Peter, Thomas. 

> > ---
> >  mm/oom_kill.c |   34 +++++++++++++++++++++++++++++++---
> >  1 files changed, 31 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index b5678bf..0858b18 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -82,6 +82,24 @@ 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))
> > +		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> > +}
> > +
> > +/*
> >   * The process p may have detached its own ->mm while exiting or through
> >   * use_mm(), but one or more of its subthreads may still have a valid
> >   * pointer.  Return p, or any of its subthreads with a valid ->mm, with
> > @@ -421,7 +439,7 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> >  }
> >  
> >  #define K(x) ((x) << (PAGE_SHIFT-10))
> > -static int oom_kill_task(struct task_struct *p)
> > +static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
> >  {
> >  	p = find_lock_task_mm(p);
> >  	if (!p) {
> > @@ -434,9 +452,17 @@ static int oom_kill_task(struct task_struct *p)
> >  		K(get_mm_counter(p->mm, MM_FILEPAGES)));
> >  	task_unlock(p);
> >  
> > -	p->rt.time_slice = HZ;
> > +
> >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> >  	force_sig(SIGKILL, p);
> > +
> > +	/*
> > +	 * 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...
> > +	 */
> > +	boost_dying_task_prio(p, mem);
> > +
> >  	return 0;
> >  }
> >  #undef K
> > @@ -460,6 +486,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> >  	 */
> >  	if (p->flags & PF_EXITING) {
> >  		set_tsk_thread_flag(p, TIF_MEMDIE);
> > +		boost_dying_task_prio(p, mem);
> >  		return 0;
> >  	}
> >  
> > @@ -489,7 +516,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> >  		}
> >  	} while_each_thread(p, t);
> >  
> > -	return oom_kill_task(victim);
> > +	return oom_kill_task(victim, mem);
> >  }
> >  
> >  /*
> > @@ -670,6 +697,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> >  	 */
> >  	if (fatal_signal_pending(current)) {
> >  		set_thread_flag(TIF_MEMDIE);
> > +		boost_dying_task_prio(current, NULL);
> >  		return;
> >  	}
> >  
> > -- 
> > 1.6.5.2
> > 
> > 
> > 
> 
> 
> 

-- 
Kind regards,
Minchan Kim

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