Re: [PATCH] mm,oom: don't kill children of oom_task_origin() process.

[Michal Hocko <mhocko@suse.cz>]

On Sat 20-02-16 13:54:02, Tetsuo Handa wrote:
> Selecting a child of the candidate which was chosen by oom_task_origin()
> is pointless. We want to kill the candidate first.

NACK, until we see a clear evidence that there is a real application
which triggers ksm/swapoff from a context where this would make a
difference. There is no good reason to add new checks to an already
subtle code just for something that even doesn't matter in the real
life.

> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
>  mm/oom_kill.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 28d6a32..703537a2 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -697,6 +697,14 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
>  	if (__ratelimit(&oom_rs))
>  		dump_header(oc, p, memcg);
>  
> +	/*
> +	 * We must send SEGKILL on p rather than p's children in order to make
> +	 * sure that oom_task_origin(p) becomes false. Printing the score value
> +	 * which is (ULONG_MAX * 1000 / totalpages) is useless for this case.
> +	 */
> +	if (oom_task_origin(p))
> +		goto kill;
> +
>  	pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
>  		message, task_pid_nr(p), p->comm, points);
>  
> @@ -728,6 +736,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
>  	}
>  	read_unlock(&tasklist_lock);
>  
> + kill:
>  	p = find_lock_task_mm(victim);
>  	if (!p) {
>  		put_task_struct(victim);
> -- 
> 1.8.3.1
> 
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-- 
Michal Hocko
SUSE Labs

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