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

[KOSAKI Motohiro]

Sorry, I forgot to cc Luis. resend.


(intentional full quote)

> From: Luis Claudio R. Goncalves <lclaudio@xxxxxxxx>
> 
> 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@xxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> ---
>  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
> 
> 
> 



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