Re: [PATCH 13 of 24] simplify oom heuristics

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 22 Aug 2007 14:49:00 +0200 Andrea Arcangeli <andrea@suse.de> wrote:

> # HG changeset patch
> # User Andrea Arcangeli <andrea@suse.de>
> # Date 1187778125 -7200
> # Node ID cd70d64570b9add8072f7abe952b34fe57c60086
> # Parent  1473d573b9ba8a913bafa42da2cac5dcca274204
> simplify oom heuristics
> 
> Over time somebody had the good idea to remove the rcvd_sigterm points,
> this removes more of them. The selected task should be the one that if
> we don't kill, it will turn the system oom again sooner than later.
> These informations tell us nothing about which task is best to kill so
> they should be removed.
> 
> Signed-off-by: Andrea Arcangeli <andrea@suse.de>
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -53,7 +53,7 @@ static unsigned long last_tif_memdie_jif
>  
>  unsigned long badness(struct task_struct *p, unsigned long uptime)
>  {
> -	unsigned long points, cpu_time, run_time, s;
> +	unsigned long points;
>  	struct mm_struct *mm;
>  	struct task_struct *child;
>  
> @@ -94,26 +94,6 @@ unsigned long badness(struct task_struct
>  			points += child->mm->total_vm/2 + 1;
>  		task_unlock(child);
>  	}
> -
> -	/*
> -	 * CPU time is in tens of seconds and run time is in thousands
> -         * of seconds. There is no particular reason for this other than
> -         * that it turned out to work very well in practice.
> -	 */
> -	cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
> -		>> (SHIFT_HZ + 3);
> -
> -	if (uptime >= p->start_time.tv_sec)
> -		run_time = (uptime - p->start_time.tv_sec) >> 10;
> -	else
> -		run_time = 0;
> -
> -	s = int_sqrt(cpu_time);
> -	if (s)
> -		points /= s;
> -	s = int_sqrt(int_sqrt(run_time));
> -	if (s)
> -		points /= s;
>  
>  	/*
>  	 * Niced processes are most likely less important, so double
> 

I think the idea behind the code which you're removing is to avoid killing
a computationally-expensive task which we've already invested a lot of CPU
time in.  IOW, kill the job which has been running for three seconds in
preference to the one which has been running three weeks.

That seems like a good strategy to me.

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