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