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

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Date:	Fri, 16 Mar 2012 22:12:55 +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 Fri, 2012-03-16 at 13:34 -0500, Christoph Lameter wrote:
> On Fri, 16 Mar 2012, Peter Zijlstra wrote:
> 
> > Add another layer of fallback policy to make the home node concept
> > useful from a memory allocation PoV.
> >
> > This changes the mpol order to:
> >
> >  - vma->vm_ops->get_policy	[if applicable]
> >  - vma->vm_policy		[if applicable]
> >  - task->mempolicy
> >  - tsk_home_node() preferred	[NEW]
> >  - default_policy
> >
> > 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.
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