Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node`

[Donald Buczek]

On 11/30/16 12:09, 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?

Wait... 21 hours is not yet a test result.

> > 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?

buczek@null:~$ zcat /proc/config.gz |grep PREE
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

Thanks
  Donald

--
Donald Buczek
buczek@xxxxxxxxxxxxx
Tel: +49 30 8413 1433