linux-kernel - Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink

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Date:   Fri, 2 Dec 2016 10:37:35 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Boris Zhmurov <bb@...nelpanic.ru>
Cc:     paulmck@...ux.vnet.ibm.com, Paul Menzel <pmenzel@...gen.mpg.de>,
        Donald Buczek <buczek@...gen.mpg.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and
 `mem_cgroup_shrink_node`

On Thu 01-12-16 21:10:01, Boris Zhmurov wrote:
> Michal Hocko 30/11/16 21:25:
> 
> >>> Do I get it right that s@...d_resched_rcu_qs@...d_resched@ didn't help?
> >>
> >> I didn't try that. I've tried 4 patches from Paul's linux-rcu tree.
> >> I can try another portion of patches, no problem :)
> > 
> > Replacing cond_resched_rcu_qs in shrink_node_memcg by cond_resched would
> > be really helpful to tell whether we are missing a real scheduling point
> > or whether something more serious is going on here.
> 
> Well, I can confirm, that replacing cond_resched_rcu_qs in
> shrink_node_memcg by cond_resched also makes dmesg clean from RCU CPU
> stall warnings.
> 
> I've attached patch (just modification of Paul's patch), that fixes RCU
> stall messages in situations, when all memory is used by
> couchbase/memcached + fs cache and linux starts to use swap.

OK, thanks for the confirmation! I will send a patch because it is true
that we do not have any scheduling point if no pages can be isolated
fromm the LRU. This might be what you are seeing.
-- 
Michal Hocko
SUSE Labs