linux-kernel - Re: [PATCH 2/4] remove boost_dying_task

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Message-Id: <20110411145832.ae133cf8.akpm@linux-foundation.org>
Date:	Mon, 11 Apr 2011 14:58:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrey Vagin <avagin@...nvz.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2/4] remove boost_dying_task_prio()

On Mon, 11 Apr 2011 14:31:18 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> This is a almost revert commit 93b43fa (oom: give the dying
> task a higher priority).
> 
> The commit dramatically improve oom killer logic when fork-bomb
> occur. But, I've found it has nasty corner case. Now cpu cgroup
> has strange default RT runtime. It's 0! That said, if a process
> under cpu cgroup promote RT scheduling class, the process never
> run at all.

hm.  How did that happen?  I thought that sched_setscheduler() modifies
only a single thread, and that thread is in the process of exiting?

> Eventually, kernel may hang up when oom kill occur.
> I and Luis who original author agreed to disable this logic at
> once.
> 
> ...
>
> index 6a819d1..83fb72c1 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -84,24 +84,6 @@ 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);
> -}

I'm rather glad to see that code go away though - SCHED_FIFO is
dangerous...
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