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

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Date:   Tue, 19 Sep 2017 11:45:21 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, memory_hotplug: do not back off draining pcp free
 pages from kworker context

On Mon 18-09-17 20:38:22, Tejun Heo wrote:
> 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.

OK, so there shouldn't be any issue with the patch, right?
-- 
Michal Hocko
SUSE Labs