linux-kernel - Re: [RFC PATCH 1/2] mm, oom: marks all killed tasks as oom victims

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Date:   Mon, 22 Oct 2018 12:43:41 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] mm, oom: marks all killed tasks as oom victims

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?
-- 
Michal Hocko
SUSE Labs