Re: [RFC PATCH 6/6] mm: Drain LRUs upon resume to userspace on nohz_full CPUs

[Michal Hocko]

On Tue 25-06-24 15:52:44, Frederic Weisbecker wrote:
> LRUs can be drained through several ways. One of them may add disturbances
> to isolated workloads while queuing a work at any time to any target,
> whether running in nohz_full mode or not.
> 
> Prevent from that on isolated tasks with draining LRUs upon resuming to
> userspace using the isolated task work framework.
> 
> It's worth noting that this is inherently racy against
> lru_add_drain_all() remotely queueing the per CPU drain work and
> therefore it prevents from the undesired disturbance only
> *most of the time*.

Can we simply not schedule flushing on remote CPUs and leave that to the
"return to the userspace" path?

I do not think we rely on LRU cache flushing for correctness purposes anywhere.

Please also CC linux MM ML once the core infrastructure is agreed on.
-- 
Michal Hocko
SUSE Labs