linux-kernel - Re: [tip:sched/numa] sched/numa: Introduce sys_numa

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Message-ID: <1337356192.573.75.camel@twins>
Date:	Fri, 18 May 2012 17:49:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Rik van Riel <riel@...hat.com>, mingo@...nel.org, hpa@...or.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	pjt@...gle.com, bharata.rao@...il.com, akpm@...ux-foundation.org,
	Lee.Schermerhorn@...com, aarcange@...hat.com, danms@...ibm.com,
	suresh.b.siddha@...el.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/numa] sched/numa: Introduce sys_numa_{t,m}bind()

On Fri, 2012-05-18 at 10:47 -0500, Christoph Lameter wrote:
> On Fri, 18 May 2012, Peter Zijlstra wrote:
> 
> > On Fri, 2012-05-18 at 17:35 +0200, Peter Zijlstra wrote:
> > > I've also said many times over that I absolutely detest all the async
> > > stuff because it messes up accounting. And until someone comes up with a
> > > sane means of sorting that I'll stick to migrate-on-fault.
> >
> > The other nice advantage of migrate-on-fault is that you don't have to
> > play lifetime games with vmas. This much simplifies that aspect.
> 
> The problem with migrate on fault in the past has been that there was no
> consistent benefit from the overhead added to the system. Useless page
> migration is a bit expensive.

I'm not sure I follow.. having the page local is a win, presuming you
can limit the migration rate to something low in relation to the cost of
remote accesses.

How does it matter how you migrate?
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