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Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates.

From David Rientjes <rientjes@google.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates.
Date 2016-01-14 02:00 +0100
Message-ID <qQEqC-7BF-9@gated-at.bofh.it> (permalink)
References (1 earlier) <qOkcH-137-25@gated-at.bofh.it> <qOkZ4-1DY-39@gated-at.bofh.it> <qOCjh-5hH-19@gated-at.bofh.it> <qQhDH-cE-1@gated-at.bofh.it> <qQrjI-6WP-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Wed, 13 Jan 2016, Tetsuo Handa wrote:

> David Rientjes wrote:
> > > @@ -171,7 +195,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
> > >  	if (oom_unkillable_task(p, memcg, nodemask))
> > >  		return 0;
> > > 
> > > -	p = find_lock_task_mm(p);
> > > +	p = find_lock_non_victim_task_mm(p);
> > >  	if (!p)
> > >  		return 0;
> > > 
> > 
> > I understand how this may make your test case pass, but I simply don't 
> > understand how this could possibly be the correct thing to do.  This would 
> > cause oom_badness() to return 0 for any process where a thread has 
> > TIF_MEMDIE set.  If the oom killer is called from the page allocator, 
> > kills a thread, and it is recalled before that thread may exit, then this 
> > will panic the system if there are no other eligible processes to kill.
> > 
> Why? oom_badness() is called after oom_scan_process_thread() returned OOM_SCAN_OK.
> oom_scan_process_thread() returns OOM_SCAN_ABORT if a thread has TIF_MEMDIE set.
> 

oom_scan_process_thread() checks for TIF_MEMDIE on p, not on p's threads.  
If one of p's threads has TIF_MEMDIE set and p does not, we actually want 
to set TIF_MEMDIE for p.  That's the current behavior since it will lead 
to p->mm memory freeing.  Your patch is excluding such processes entirely 
and selecting another process to kill unnecessarily.

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Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Michal Hocko <mhocko@kernel.org> - 2016-01-07 10:20 +0100
  Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-07 14:40 +0100
    Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Michal Hocko <mhocko@kernel.org> - 2016-01-07 16:00 +0100
      Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-07 16:40 +0100
        Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Michal Hocko <mhocko@kernel.org> - 2016-01-11 16:20 +0100
          Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-12 12:40 +0100
            Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Michal Hocko <mhocko@kernel.org> - 2016-01-12 21:00 +0100
              Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-13 11:20 +0100
                Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Michal Hocko <mhocko@kernel.org> - 2016-01-13 16:30 +0100
      Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Michal Hocko <mhocko@kernel.org> - 2016-01-07 16:50 +0100
        Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-08 11:20 +0100
          Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from  candidates. David Rientjes <rientjes@google.com> - 2016-01-13 01:40 +0100
            Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-13 12:00 +0100
              Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from  candidates. David Rientjes <rientjes@google.com> - 2016-01-14 02:00 +0100
                Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-14 11:30 +0100
                Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from  candidates. David Rientjes <rientjes@google.com> - 2016-01-14 23:00 +0100
                Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-01-14 23:30 +0100

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