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Date:   Tue, 10 Jul 2018 11:55:21 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Michal Hocko <mhocko@kernel.org>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm, oom: remove sleep from under oom_lock
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On Tue, 10 Jul 2018, Michal Hocko wrote:

> What do you think about the following?
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index ed9d473c571e..32e6f7becb40 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -53,6 +53,14 @@ int sysctl_panic_on_oom;
>  int sysctl_oom_kill_allocating_task;
>  int sysctl_oom_dump_tasks = 1;
>  
> +/*
> + * Serializes oom killer invocations (out_of_memory()) from all contexts to
> + * prevent from over eager oom killing (e.g. when the oom killer is invoked
> + * from different domains).
> + *
> + * oom_killer_disable() relies on this lock to stabilize oom_killer_disabled
> + * and mark_oom_victim
> + */
>  DEFINE_MUTEX(oom_lock);
>  
>  #ifdef CONFIG_NUMA

I think it's better, thanks.  However, does it address the question about 
why __oom_reap_task_mm() needs oom_lock protection?  Perhaps it would be 
helpful to mention synchronization between reaping triggered from 
oom_reaper and by exit_mmap().