Re: [PATCH] mm, memory_hotplug: do not back off draining pcp free pages from kworker context

From: Tejun Heo
Date: Mon Sep 18 2017 - 23:38:51 EST

Hello, Sorry about the delay.

On Thu, Aug 31, 2017 at 07:33:42AM +0200, Michal Hocko wrote:
> > > Michal, are you sure that this patch does not cause deadlock?
> > >
> > > As shown in "[PATCH] mm: Use WQ_HIGHPRI for mm_percpu_wq." thread, currently work
> > > items on mm_percpu_wq seem to be blocked by other work items not on mm_percpu_wq.

IIUC that wasn't a deadlock but more a legitimate starvation from too
many tasks trying to reclaim directly.

> > But we have a rescuer so we should make a forward progress eventually.
> > Or am I missing something. Tejun, could you have a look please?
> ping... I would really appreaciate if you could double check my thinking
> Tejun. This is a tricky area and I would like to prevent further subtle
> issues here.

So, this shouldn't be an issue. This may get affected by direct
reclaim frenzy but it's only a small piece of the whole symptom and we
gotta fix that at the source.