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Date: Wed, 8 Nov 2017 16:03:18 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 4/5] mm,oom: Remove oom_lock serialization from the OOM
 reaper.
Message-ID: <20171108150318.amgwclu6yecssafe@dhcp22.suse.cz>
References: <1510138908-6265-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
 <1510138908-6265-4-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
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Sender: owner-linux-mm@kvack.org
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org

Thank you for CCing me (as an author of the code)

On Wed 08-11-17 20:01:47, Tetsuo Handa wrote:
> Since "mm,oom: Move last second allocation to inside the OOM killer."
> changed to do last second allocation attempt after confirming that there
> is no OOM victim's mm without MMF_OOM_SKIP set, we no longer need to
> block the OOM reaper using oom_lock. This patch should allow start
> reclaiming earlier than now.
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/oom_kill.c | 17 -----------------
>  1 file changed, 17 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index cf6f19b..6949465 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -495,22 +495,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
>  	struct vm_area_struct *vma;
>  	bool ret = true;
>  
> -	/*
> -	 * We have to make sure to not race with the victim exit path
> -	 * and cause premature new oom victim selection:
> -	 * __oom_reap_task_mm		exit_mm
> -	 *   mmget_not_zero
> -	 *				  mmput
> -	 *				    atomic_dec_and_test
> -	 *				  exit_oom_victim
> -	 *				[...]
> -	 *				out_of_memory
> -	 *				  select_bad_process
> -	 *				    # no TIF_MEMDIE task selects new victim
> -	 *  unmap_page_range # frees some memory
> -	 */
> -	mutex_lock(&oom_lock);
> -
>  	if (!down_read_trylock(&mm->mmap_sem)) {
>  		ret = false;
>  		trace_skip_task_reaping(tsk->pid);
> @@ -584,7 +568,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
>  
>  	trace_finish_task_reaping(tsk->pid);
>  unlock_oom:
> -	mutex_unlock(&oom_lock);
>  	return ret;
>  }
>  
> -- 
> 1.8.3.1
> 
> --
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-- 
Michal Hocko
SUSE Labs

--
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