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 05:52:16 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Boris Zhmurov <bb@...nelpanic.ru>,
        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 Fri, Dec 02, 2016 at 10:37:35AM +0100, Michal Hocko wrote:
> 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.

Thank you both!

							Thanx, Paul