From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Donald Buczek <buczek@molgen.mpg.de>,
Paul Menzel <pmenzel@molgen.mpg.de>,
dvteam@molgen.mpg.de, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Josh Triplett <josh@joshtriplett.org>
Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node`
Date: Wed, 30 Nov 2016 03:54:42 -0800 [thread overview]
Message-ID: <20161130115442.GA19271@linux.vnet.ibm.com> (raw)
In-Reply-To: <20161130115320.GO3924@linux.vnet.ibm.com>
On Wed, Nov 30, 2016 at 03:53:20AM -0800, Paul E. McKenney wrote:
> On Wed, Nov 30, 2016 at 12:09:44PM +0100, Michal Hocko wrote:
> > [CCing Paul]
> >
> > On Wed 30-11-16 11:28:34, Donald Buczek wrote:
> > [...]
> > > shrink_active_list gets and releases the spinlock and calls cond_resched().
> > > This should give other tasks a chance to run. Just as an experiment, I'm
> > > trying
> > >
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -1921,7 +1921,7 @@ static void shrink_active_list(unsigned long
> > > nr_to_scan,
> > > spin_unlock_irq(&pgdat->lru_lock);
> > >
> > > while (!list_empty(&l_hold)) {
> > > - cond_resched();
> > > + cond_resched_rcu_qs();
> > > page = lru_to_page(&l_hold);
> > > list_del(&page->lru);
> > >
> > > and didn't hit a rcu_sched warning for >21 hours uptime now. We'll see.
> >
> > This is really interesting! Is it possible that the RCU stall detector
> > is somehow confused?
>
> No, it is not confused. Again, cond_resched() is not a quiescent
> state unless it does a context switch. Therefore, if the task running
> in that loop was the only runnable task on its CPU, cond_resched()
> would -never- provide RCU with a quiescent state.
>
> In contrast, cond_resched_rcu_qs() unconditionally provides RCU
> with a quiescent state (hence the _rcu_qs in its name), regardless
> of whether or not a context switch happens.
>
> It is therefore expected behavior that this change might prevent
> RCU CPU stall warnings.
I should add... This assumes that CONFIG_PREEMPT=n. So what is
CONFIG_PREEMPT?
Thanx, Paul
> > > Is preemption disabled for another reason?
> >
> > I do not think so. I will have to double check the code but this is a
> > standard sleepable context. Just wondering what is the PREEMPT
> > configuration here?
> > --
> > Michal Hocko
> > SUSE Labs
> >
next prev parent reply other threads:[~2016-11-30 11:55 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <24c226a5-1a4a-173e-8b4e-5107a2baac04@molgen.mpg.de>
2016-11-08 12:22 ` INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Paul Menzel
2016-11-08 17:03 ` Paul E. McKenney
2016-11-08 17:38 ` Paul Menzel
2016-11-08 18:39 ` Paul E. McKenney
2016-11-16 17:01 ` Paul Menzel
2016-11-16 17:30 ` Paul E. McKenney
2016-11-21 13:41 ` Michal Hocko
2016-11-21 14:01 ` Paul E. McKenney
2016-11-21 14:18 ` Michal Hocko
2016-11-21 14:29 ` Paul E. McKenney
2016-11-21 15:35 ` Donald Buczek
2016-11-24 10:15 ` Michal Hocko
2016-11-24 18:50 ` Donald Buczek
2016-11-27 9:37 ` Paul Menzel
2016-11-27 5:32 ` Christopher S. Aker
2016-11-27 9:19 ` Donald Buczek
2016-11-28 11:04 ` Michal Hocko
2016-11-28 12:26 ` Paul Menzel
2016-11-30 10:28 ` Donald Buczek
2016-11-30 11:09 ` Michal Hocko
2016-11-30 11:43 ` Donald Buczek
2016-12-02 9:14 ` Donald Buczek
2016-12-06 8:32 ` Donald Buczek
2016-11-30 11:53 ` Paul E. McKenney
2016-11-30 11:54 ` Paul E. McKenney [this message]
2016-11-30 12:31 ` Paul Menzel
2016-11-30 14:31 ` Paul E. McKenney
2016-11-30 13:19 ` Michal Hocko
2016-11-30 14:29 ` Paul E. McKenney
2016-11-30 16:38 ` Peter Zijlstra
2016-11-30 17:02 ` Paul E. McKenney
2016-11-30 17:05 ` Michal Hocko
2016-11-30 17:23 ` Paul E. McKenney
2016-11-30 17:34 ` Michal Hocko
2016-11-30 17:50 ` Peter Zijlstra
2016-11-30 19:40 ` Paul E. McKenney
2016-12-01 5:30 ` Peter Zijlstra
2016-12-01 12:40 ` Paul E. McKenney
2016-12-01 16:36 ` Peter Zijlstra
2016-12-01 16:59 ` Paul E. McKenney
2016-12-01 18:09 ` Peter Zijlstra
2016-12-01 18:42 ` Paul E. McKenney
2016-12-01 18:49 ` Peter Zijlstra
[not found] <20161125212000.GI31360@linux.vnet.ibm.com>
[not found] ` <20161128095825.GI14788@dhcp22.suse.cz>
[not found] ` <20161128105425.GY31360@linux.vnet.ibm.com>
[not found] ` <3a4242cb-0198-0a3b-97ae-536fb5ff83ec@kernelpanic.ru>
[not found] ` <20161128143435.GC3924@linux.vnet.ibm.com>
[not found] ` <eba1571e-f7a8-09b3-5516-c2bc35b38a83@kernelpanic.ru>
[not found] ` <20161128150509.GG3924@linux.vnet.ibm.com>
[not found] ` <66fd50e1-a922-846a-f427-7654795bd4b5@kernelpanic.ru>
[not found] ` <20161130174802.GM18432@dhcp22.suse.cz>
[not found] ` <fd34243c-2ebf-c14b-55e6-684a9dc614e7@kernelpanic.ru>
[not found] ` <20161130182552.GN18432@dhcp22.suse.cz>
2016-12-01 18:10 ` Boris Zhmurov
2016-12-01 19:39 ` Paul E. McKenney
2016-12-02 9:37 ` Michal Hocko
2016-12-02 13:52 ` Paul E. McKenney
2016-12-02 16:39 ` Boris Zhmurov
2016-12-02 16:44 ` Paul E. McKenney
2016-12-02 17:02 ` Michal Hocko
2016-12-02 17:15 ` Paul E. McKenney
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