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

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Message-ID: <20151027120704.GF9891@dhcp22.suse.cz>
Date:	Tue, 27 Oct 2015 13:07:04 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tejun Heo <htejun@...il.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, cl@...ux.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, 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 Tue 27-10-15 19:55:06, Tejun Heo wrote:
> On Tue, Oct 27, 2015 at 10:22:31AM +0100, Michal Hocko wrote:
> ...
> > stable kernels without causing any other regressions. 2) is the way
> > to move forward for next kernels and we should really think whether
> > WQ_MEM_RECLAIM should imply also WQ_HIGHPRI by default. If there is a
> > general consensus that there are legitimate WQ_MEM_RECLAIM users which
> > can do without the other flag then I am perfectly OK to use it for
> > vmstat and oom sysrq dedicated workqueues.
> 
> I don't think flagging these things is a good approach.  These are too
> easy to miss.  If this is a problem which needs to be solved, which
> I'm not convined it is at this point, the right thing to do would be
> doing stall detection and kicking the next work item automatically.

To be honest, I do not really care whether this gets "fixed" in the
stall detection code or by making WQ_MEM_RECLAIM to flag a special
behavior implicitly. All I would like to see is to have a guarantee
that such workqueues are not staying behind just because all current
workers are in the allocator. Adding artificial schedule_timeouts in the
allocator is a fragile way to work around the issue.
-- 
Michal Hocko
SUSE Labs
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