linux-kernel - Re: [RFC][PATCH 10/26] mm, mpol: Make mempolicy home-node aware

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Message-ID: <1332165959.18960.340.camel@twins>
Date:	Mon, 19 Mar 2012 15:05:59 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 10/26] mm, mpol: Make mempolicy home-node aware

On Mon, 2012-03-19 at 08:53 -0500, Christoph Lameter wrote:
> On Fri, 16 Mar 2012, Peter Zijlstra wrote:
> 
> > > > Note that the tsk_home_node() policy has Migrate-on-Fault enabled to
> > > > facilitate efficient on-demand memory migration.
> > >
> > > The numa hierachy is already complex. Could we avoid adding another layer
> > > by adding a MPOL_HOME_NODE and make that the default?
> >
> > Not sure that's really a win, the behaviour would be the same we just
> > have to implement another policy, which is likely more code.
> 
> A HOME_NODE policy would also help to ensure that existing applications
> continue to work as expected. Given that people in the HPC industry and
> elsewhere have been fine tuning around the scheduler for years this is a
> desirable goal and ensures backward compatibility.

I really have no idea what you're saying. Existing applications that use
mbind/set_mempolicy already continue to function exactly like before,
see how the new layer is below all that.


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