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

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Message-ID: <20151022150623.GE26854@dhcp22.suse.cz>
Date:	Thu, 22 Oct 2015 17:06:23 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Tejun Heo <htejun@...il.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	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 22-10-15 23:09:44, 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.

Do I get it right that if vmstat_update has its own workqueue with
WQ_MEM_RECLAIM then there is a _guarantee_ that the rescuer will always
be able to process vmstat_update work from the requested CPU?

That should be sufficient because vmstat_update doesn't sleep on
allocation. I agree that this would be a more appropriate fix.

-- 
Michal Hocko
SUSE Labs
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