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

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Date:	Fri, 27 Mar 2015 06:11:44 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>, hannes@...xchg.org,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vinmenon@...eaurora.org, shashim@...eaurora.org,
	Michal Hocko <mhocko@...e.cz>, 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 Fri, 27 Mar 2015, Peter Zijlstra wrote:

> > We could align the base on 8 bytes to gain an extra bit in the pointer
> > and use that bit to indicate the running state. Then these sites can
> > spin on that bit while we can change the actual base pointer.
>
> Even though tvec_base has ____cacheline_aligned stuck on, most are
> allocated using kzalloc_node() which does not actually respect that but
> already guarantees a minimum u64 alignment, so I think we can use that
> third bit without too much magic.

Create a new slab cache for this purpose that does the proper aligning?

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