linux-kernel - Re: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work

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Message-ID: <20150330150818.GE3909@dhcp22.suse.cz>
Date:	Mon, 30 Mar 2015 17:08:18 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>, hannes@...xchg.org,
	Christoph Lameter <cl@...ux.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vinmenon@...eaurora.org, shashim@...eaurora.org, mgorman@...e.de,
	dave@...olabs.net, koct9i@...il.com,
	Linux Memory Management List <linux-mm@...ck.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work

On Sat 28-03-15 10:53:22, Peter Zijlstra wrote:
[...]
> Alternatively the thing hocko suggests is an utter fail too. You cannot
> stuff that into hardirq context, that's insane.

I guess you are referring to
http://article.gmane.org/gmane.linux.kernel.mm/127569, right?

Why cannot we do something like refresh_cpu_vm_stats from the IRQ
context?  Especially the first zone stat part. The per-cpu pagesets is
more costly and it would need a special treatment, alright. A simple
way would be to splice the lists from the per-cpu context and then free
those pages from the kthread context.

I am still wondering why those two things were squashed into a single
place. Why kswapd is not doing the pcp cleanup?
-- 
Michal Hocko
SUSE Labs
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