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

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Message-ID: <20151022142155.GB30579@mtj.duckdns.org>
Date:	Thu, 22 Oct 2015 23:21:55 +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

On Thu, Oct 22, 2015 at 11:09:44PM +0900, Tejun Heo wrote:
> On Thu, Oct 22, 2015 at 08:39:11AM -0500, Christoph Lameter wrote:
> > On Thu, 22 Oct 2015, Tetsuo Handa wrote:
> > 
> > > The problem would be that the "struct task_struct" to execute vmstat_update
> > > job does not exist, and will not be able to create one on demand because we
> > > are stuck at __GFP_WAIT allocation. Therefore adding a dedicated kernel
> > > thread for vmstat_update job would work. But ...
> > 
> > Yuck. Can someone please get this major screwup out of the work queue
> > subsystem? Tejun?
> 
> Hmmm?  Just use a dedicated workqueue with WQ_MEM_RECLAIM.  If
> concurrency management is a problem and there's something live-locking
> for that work item (really?), WQ_CPU_INTENSIVE escapes it.  If this is
> a common occurrence that it makes sense to give vmstat higher
> priority, set WQ_HIGHPRI.

Oooh, HIGHPRI + CPU_INTENSIVE immediate scheduling guarantee got lost
while converting HIGHPRI to a separate pool but guaranteeing immediate
scheduling for CPU_INTENSIVE is trivial.  If vmstat requires that,
please let me know.

Thanks.

-- 
tejun
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