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

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Date:	Sat, 24 Oct 2015 03:21:09 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Michal Hocko <mhocko@...nel.org>
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

Hello,

On Fri, Oct 23, 2015 at 01:11:45PM +0200, Michal Hocko wrote:
> > The problem here is not lack
> > of execution resource but concurrency management misunderstanding the
> > situation. 
> 
> And this sounds like a bug to me.

I don't know.  I can be argued either way, the other direction being a
kernel thread going RUNNING non-stop is buggy.  Given how this has
been a complete non-issue for all the years, I'm not sure how useful
plugging this is.

> Don't we have some IO related paths which would suffer from the same
> problem. I haven't checked all the WQ_MEM_RECLAIM users but from the
> name I would expect they _do_ participate in the reclaim and so they
> should be able to make a progress. Now if your new IMMEDIATE flag will

Seriously, nobody goes full-on RUNNING.

> guarantee that then I would argue that it should be implicit for
> WQ_MEM_RECLAIM otherwise we always risk a similar situation. What would
> be a counter argument for doing that?

Not serving any actual purpose and degrading execution behavior.

Thanks.

-- 
tejun
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