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

[Peter Zijlstra]

On Thu, Dec 01, 2016 at 04:40:24AM -0800, Paul E. McKenney wrote:
> On Thu, Dec 01, 2016 at 06:30:35AM +0100, Peter Zijlstra wrote:

> > Sure, we all dislike IPIs, but I'm thinking this half-way point is
> > sensible, no point in issuing user visible annoyance if indeed we can
> > prod things back to life, no?
> > 
> > Only if we utterly fail to make it respond should we bug the user with
> > our failure..
> 
> Sold!  ;-)
> 
> I will put together a patch later today.
> 
> My intent is to hold off on the "upgrade cond_resched()" patch, one
> step at a time.  Longer term, I do very much like the idea of having
> cond_resched() do both scheduling and RCU quiescent states, assuming
> that this avoids performance pitfalls.

Well, with the above change cond_resched() is already sufficient, no?

In fact, by doing the IPI thing we get the entire cond_resched*()
family, and we could add the should_resched() guard to
cond_resched_rcu().