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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
Date: Wed, 11 Mar 2020 12:38:07 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.21.2003111235080.171292@chino.kir.corp.google.com> (raw)
In-Reply-To: <7a6170fc-b247-e327-321a-b99fb53f552d@i-love.sakura.ne.jp>

On Wed, 11 Mar 2020, Tetsuo Handa wrote:

> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >>> --- a/mm/vmscan.c
> >>> +++ b/mm/vmscan.c
> >>> @@ -2637,6 +2637,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
> >>>  		unsigned long reclaimed;
> >>>  		unsigned long scanned;
> >>>  
> >>> +		cond_resched();
> >>> +
> >>
> >> Is this safe for CONFIG_PREEMPTION case? If current thread has realtime priority,
> >> can we guarantee that the OOM victim (well, the OOM reaper kernel thread rather
> >> than the OOM victim ?) gets scheduled?
> >>
> > 
> > I think it's the best we can do that immediately solves the issue unless 
> > you have another idea in mind?
> 
> "schedule_timeout_killable(1) outside of oom_lock" or "the OOM reaper grabs oom_lock
> so that allocating threads guarantee that the OOM reaper gets scheduled" or "direct OOM
> reaping so that allocating threads guarantee that some memory is reclaimed".
> 

The cond_resched() here is needed if the iteration is lengthy depending on 
the number of descendant memcgs already.

schedule_timeout_killable(1) does not make any guarantees that current 
will be scheduled after the victim or oom_reaper on UP systems.

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.

> > 
> >>>  		switch (mem_cgroup_protected(target_memcg, memcg)) {
> >>>  		case MEMCG_PROT_MIN:
> >>>  			/*
> >>>
> >>
> 
> 

  reply	other threads:[~2020-03-11 19:38 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-10 21:39 [patch] mm, oom: prevent soft lockup on memcg oom for UP systems David Rientjes
2020-03-10 22:05 ` Tetsuo Handa
2020-03-10 22:55   ` David Rientjes
2020-03-11  9:34     ` Tetsuo Handa
2020-03-11 19:38       ` David Rientjes [this message]
2020-03-11 22:04         ` Tetsuo Handa
2020-03-11 22:14           ` David Rientjes
2020-03-12  0:12             ` Tetsuo Handa
2020-03-12 18:07               ` David Rientjes
2020-03-12 22:32                 ` Andrew Morton
2020-03-16  9:31                   ` Michal Hocko
2020-03-16 10:04                     ` Tetsuo Handa
2020-03-16 10:14                       ` Michal Hocko
2020-03-13  0:15                 ` Tetsuo Handa
2020-03-13 22:01                   ` David Rientjes
2020-03-13 23:15                     ` Tetsuo Handa
2020-03-13 23:32                       ` Tetsuo Handa
2020-03-16 23:59                         ` David Rientjes
2020-03-17  3:18                           ` Tetsuo Handa
2020-03-17  4:09                             ` David Rientjes
2020-03-18  0:55                               ` [patch v2] " David Rientjes
2020-03-18  9:42                                 ` Michal Hocko
2020-03-18 21:40                                   ` David Rientjes
2020-03-18 22:03                                     ` [patch v3] " David Rientjes
2020-03-19  7:09                                       ` Michal Hocko
2020-03-12  4:23             ` [patch] " Tetsuo Handa
2020-03-10 22:10 ` Michal Hocko
2020-03-10 23:02   ` David Rientjes
2020-03-11  8:27     ` Michal Hocko
2020-03-11 19:45       ` David Rientjes
2020-03-12  8:32         ` Michal Hocko
2020-03-12 18:20           ` David Rientjes
2020-03-12 20:16             ` Michal Hocko
2020-03-16  9:32               ` Michal Hocko
2020-03-11  0:18 ` Andrew Morton
2020-03-11  0:34   ` David Rientjes
2020-03-11  8:36   ` Michal Hocko

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