linux-kernel - Re: [PATCH 2/2] oom-clear-tif_memdie-after-oom_reaper-managed-to-unmap-the-address-space-fix

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Message-Id: <201603100721.CDC86433.OMFOVOHSJFLFQt@I-love.SAKURA.ne.jp>
Date:	Thu, 10 Mar 2016 07:21:58 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	akpm@...ux-foundation.org, mhocko@...nel.org
Cc:	linux-mm@...ck.org, rientjes@...gle.com,
	linux-kernel@...r.kernel.org, mhocko@...e.com, hannes@...xchg.org
Subject: Re: [PATCH 2/2] oom-clear-tif_memdie-after-oom_reaper-managed-to-unmap-the-address-space-fix

Andrew Morton wrote:
> I found the below patch lying around but I didn't queue it properly. 
> Is it legit?

I think that patch wants patch description updated.
Not testing pure noise, but causing possible livelock.
http://lkml.kernel.org/r/20160217143917.GP29196@dhcp22.suse.cz

> 
> 
> From: Johannes Weiner <hannes@...xchg.org>
> Subject: oom-clear-tif_memdie-after-oom_reaper-managed-to-unmap-the-address-space-fix
> 
> When the OOM killer scans tasks and encounters a PF_EXITING one, it
> force-selects that one regardless of the score. Is there a possibility
> that the task might hang after it has set PF_EXITING? In that case the
> OOM killer should be able to move on to the next task.
> 
> Frankly, I don't even know why we check for exiting tasks in the OOM
> killer. We've tried direct reclaim at least 15 times by the time we
> decide the system is OOM, there was plenty of time to exit and free
> memory; and a task might exit voluntarily right after we issue a kill.
> This is testing pure noise.
> 
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Andrea Argangeli <andrea@...nel.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Sasha Levin <sasha.levin@...cle.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  mm/oom_kill.c |    3 ---
>  1 file changed, 3 deletions(-)
> 
> diff -puN mm/oom_kill.c~oom-clear-tif_memdie-after-oom_reaper-managed-to-unmap-the-address-space-fix mm/oom_kill.c
> --- a/mm/oom_kill.c~oom-clear-tif_memdie-after-oom_reaper-managed-to-unmap-the-address-space-fix
> +++ a/mm/oom_kill.c
> @@ -292,9 +292,6 @@ enum oom_scan_t oom_scan_process_thread(
>  	if (oom_task_origin(task))
>  		return OOM_SCAN_SELECT;
>  
> -	if (task_will_free_mem(task) && !is_sysrq_oom(oc))
> -		return OOM_SCAN_ABORT;
> -
>  	return OOM_SCAN_OK;
>  }
>  
> _
> 
>