linux-kernel - Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates.

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Message-Id: <201601080038.CIF04698.VFJHSOQLOFFMOt@I-love.SAKURA.ne.jp>
Date:	Fri, 8 Jan 2016 00:38:43 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org
Cc:	rientjes@...gle.com, akpm@...ux-foundation.org, mgorman@...e.de,
	torvalds@...ux-foundation.org, oleg@...hat.com, hughd@...gle.com,
	andrea@...nel.org, riel@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates.

Michal Hocko wrote:
> @@ -333,6 +333,14 @@ static struct task_struct *select_bad_process(struct oom_control *oc,
>  		if (points == chosen_points && thread_group_leader(chosen))
>  			continue;
>  
> +		/*
> +		 * If the current major task is already ooom killed and this
> +		 * is sysrq+f request then we rather choose somebody else
> +		 * because the current oom victim might be stuck.
> +		 */
> +		if (is_sysrq_oom(sc) && test_tsk_thread_flag(p, TIF_MEMDIE))
> +			continue;
> +
>  		chosen = p;
>  		chosen_points = points;
>  	}

Do we want to require SysRq-f for each thread in a process?
If g has 1024 p, dump_tasks() will do

  pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu         %5hd %s\n",

for 1024 times? I think one SysRq-f per one process is sufficient.

How can we guarantee that find_lock_task_mm() from oom_kill_process()
chooses !TIF_MEMDIE thread when try_to_sacrifice_child() somehow chose
!TIF_MEMDIE thread? I think choosing !TIF_MEMDIE thread at
find_lock_task_mm() is the simplest way.
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