linux-kernel - Re: [PATCH] mm,vmscan: Use accurate values for zone

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Message-ID: <20151022151414.GF30579@mtj.duckdns.org>
Date:	Fri, 23 Oct 2015 00:14:14 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	mhocko@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	David Rientjes <rientjes@...gle.com>, oleg@...hat.com,
	kwalker@...hat.com, akpm@...ux-foundation.org, hannes@...xchg.org,
	vdavydov@...allels.com, skozina@...hat.com, mgorman@...e.de,
	riel@...hat.com
Subject: Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable()
 checks

Hello,

On Thu, Oct 22, 2015 at 09:41:11AM -0500, Christoph Lameter wrote:
> > If this is actually a legit busy-waiting cyclic dependency, just let
> > me know.
> 
> There is no dependency of the vmstat updater on anything.
> They can run anytime. If there is a dependency then its created by the
> kworker subsystem itself.

Sure, the other direction is from workqueue concurrency detection.  I
was asking whether a work item can busy-wait on vmstat_update work
item cuz that's what confuses workqueue.  Looking at the original
dump, the pool has two idle workers indicating that the workqueue
wasn't short of execution resources and it really looks like that work
item was live-locking the pool.  I'll go ahead and add WQ_IMMEDIATE.

Thanks.

-- 
tejun
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