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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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        Bharata B Rao <bharata.rao@gmail.com>,
        Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
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Date: Fri, 16 Mar 2012 22:12:55 +0100
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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.