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Date:   Wed, 11 Mar 2020 15:14:39 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [patch] mm, oom: prevent soft lockup on memcg oom for UP
 systems
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On Thu, 12 Mar 2020, Tetsuo Handa wrote:

> > The cond_resched() here is needed if the iteration is lengthy depending on 
> > the number of descendant memcgs already.
> 
> No. cond_resched() here will become no-op if CONFIG_PREEMPTION=y and current
> thread has realtime priority.
> 

It's helpful without CONFIG_PREEMPTION for excessively long memcg 
iterations to avoid starving need_resched.

> > schedule_timeout_killable(1) does not make any guarantees that current 
> > will be scheduled after the victim or oom_reaper on UP systems.
> 
> The point of schedule_timeout_*(1) is to guarantee that current thread
> will yield CPU to other threads even if CONFIG_PREEMPTION=y and current
> thread has realtime priority case. There is no guarantee that current
> thread will be rescheduled immediately after a sleep is irrelevant.
> 
> > 
> > If you have an alternate patch to try, we can test it.  But since this 
> > cond_resched() is needed anyway, I'm not sure it will change the result.
> 
> schedule_timeout_killable(1) is an alternate patch to try; I don't think
> that this cond_resched() is needed anyway.
> 

You are suggesting schedule_timeout_killable(1) in shrink_node_memcgs()?