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

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Message-ID: <20170919033821.GR378890@devbig577.frc2.facebook.com>
Date:   Mon, 18 Sep 2017 20:38:22 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Michal Hocko <mhocko@...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

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.

Thanks.

-- 
tejun