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Date: Tue, 29 Aug 2017 07:33:19 -0700
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] mm: Use WQ_HIGHPRI for mm_percpu_wq.
Message-ID: <20170829143319.GJ491396@devbig577.frc2.facebook.com>
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To: Michal Hocko <mhocko@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, akpm@linux-foundation.org, linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>

Hello,

On Tue, Aug 29, 2017 at 03:33:25PM +0200, Michal Hocko wrote:
> Hmm, we have this in should_reclaim_retry
> 			/*
> 			 * Memory allocation/reclaim might be called from a WQ
> 			 * context and the current implementation of the WQ
> 			 * concurrency control doesn't recognize that
> 			 * a particular WQ is congested if the worker thread is
> 			 * looping without ever sleeping. Therefore we have to
> 			 * do a short sleep here rather than calling
> 			 * cond_resched().
> 			 */
> 			if (current->flags & PF_WQ_WORKER)
> 				schedule_timeout_uninterruptible(1);
> 
> And I thought it would be susfficient for kworkers for concurrency WQ
> congestion thingy to jump in. Or do we need something more generic. E.g.
> make cond_resched special for kworkers?

I actually think we're hitting a bug somewhere.  Tetsuo's trace with
the patch applies doesn't add up.

Thanks.

-- 
tejun

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