linux-kernel - Re: [PATCH v2] mm,oom: exclude oom_task_origin processes if they are OOM-unkillable.

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Date:	Wed, 17 Feb 2016 14:31:54 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
cc:	mhocko@...nel.org, akpm@...ux-foundation.org, mgorman@...e.de,
	oleg@...hat.com, torvalds@...ux-foundation.org, hughd@...gle.com,
	andrea@...nel.org, riel@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm,oom: exclude oom_task_origin processes if they
 are OOM-unkillable.

On Wed, 17 Feb 2016, Tetsuo Handa wrote:

> oom_scan_process_thread() returns OOM_SCAN_SELECT when there is a
> thread which returns oom_task_origin() == true. But it is possible
> that such thread is marked as OOM-unkillable. In that case, the OOM
> killer must not select such process.
> 
> Since it is meaningless to return OOM_SCAN_OK for OOM-unkillable
> process because subsequent oom_badness() call will return 0, this
> patch changes oom_scan_process_thread to return OOM_SCAN_CONTINUE
> if that process is marked as OOM-unkillable (regardless of
> oom_task_origin()).
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Suggested-by: Michal Hocko <mhocko@...nel.org>
> ---
>  mm/oom_kill.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 7653055..cf87153 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -282,7 +282,7 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
>  		if (!is_sysrq_oom(oc))
>  			return OOM_SCAN_ABORT;
>  	}
> -	if (!task->mm)
> +	if (!task->mm || task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
>  		return OOM_SCAN_CONTINUE;
>  
>  	/*

I'm getting multiple emails from you with the identical patch, something 
is definitely wacky in your toolchain.

Anyway, this is NACK'd since task->signal->oom_score_adj is checked under 
task_lock() for threads with memory attached, that's the purpose of 
finding the correct thread in oom_badness() and taking task_lock().  We 
aren't going to duplicate logic in several functions that all do the same 
thing.