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Date:   Mon, 22 Oct 2018 13:12:29 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
        David Rientjes <rientjes@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 1/2] mm, oom: marks all killed tasks as oom victims
Message-ID: <20181022111229.GZ18839@dhcp22.suse.cz>
References: <20181022071323.9550-1-mhocko@kernel.org>
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 <201810220758.w9M7wojE016890@www262.sakura.ne.jp>
 <20181022084842.GW18839@dhcp22.suse.cz>
 <f5b257f9-47a5-e071-02fa-ce901bd34b04@i-love.sakura.ne.jp>
 <20181022104341.GY18839@dhcp22.suse.cz>
 <93f99371-cff8-fc31-a594-eecdff299f16@i-love.sakura.ne.jp>
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On Mon 22-10-18 19:56:49, Tetsuo Handa wrote:
> On 2018/10/22 19:43, Michal Hocko wrote:
> > On Mon 22-10-18 18:42:30, Tetsuo Handa wrote:
> >> On 2018/10/22 17:48, Michal Hocko wrote:
> >>> On Mon 22-10-18 16:58:50, Tetsuo Handa wrote:
> >>>> Michal Hocko wrote:
> >>>>> --- a/mm/oom_kill.c
> >>>>> +++ b/mm/oom_kill.c
> >>>>> @@ -898,6 +898,7 @@ static void __oom_kill_process(struct task_struct *victim)
> >>>>>  		if (unlikely(p->flags & PF_KTHREAD))
> >>>>>  			continue;
> >>>>>  		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, PIDTYPE_TGID);
> >>>>> +		mark_oom_victim(p);
> >>>>>  	}
> >>>>>  	rcu_read_unlock();
> >>>>>  
> >>>>> -- 
> >>>>
> >>>> Wrong. Either
> >>>
> >>> You are right. The mm might go away between process_shares_mm and here.
> >>> While your find_lock_task_mm would be correct I believe we can do better
> >>> by using the existing mm that we already have. I will make it a separate
> >>> patch to clarity.
> >>
> >> Still wrong. p->mm == NULL means that we are too late to set TIF_MEMDIE
> >> on that thread. Passing non-NULL mm to mark_oom_victim() won't help.
> > 
> > Why would it be too late? Or in other words why would this be harmful?
> > 
> 
> Setting TIF_MEMDIE after exit_mm() completed is too late.

You are right and I am obviously dense today. I will go with
find_lock_task_mm for now and push the "get rid of TIF_MEMDIE" up in the
todo list. I hope I will get to it some day.
-- 
Michal Hocko
SUSE Labs