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Date: Tue, 8 Apr 2014 19:30:31 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for
 _PAGE_NUMA v2
Message-ID: <20140408173031.GS10526@twins.programming.kicks-ass.net>
References: <1396962570-18762-1-git-send-email-mgorman@suse.de>
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To: Mel Gorman <mgorman@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, "H. Peter Anvin" <hpa@zytor.com>, Linux-X86 <x86@kernel.org>, Cyrill Gorcunov <gorcunov@gmail.com>, Ingo Molnar <mingo@kernel.org>, Steven Noonan <steven@uplinklabs.net>, Rik van Riel <riel@redhat.com>, David Vrabel <david.vrabel@citrix.com>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Dave Hansen <dave.hansen@intel.com>, Srikar Dronamraju <srikar@linux.vnet.ibm.com>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>

On Tue, Apr 08, 2014 at 05:46:52PM +0100, Mel Gorman wrote:
> Someone will ask why automatic NUMA balancing hints do not use "real"
> PROT_NONE but as it would need VMA information to do that on all
> architectures it would mean that VMA-fixups would be required when marking
> PTEs for NUMA hinting faults so would be expensive.

Like this:

  https://lkml.org/lkml/2012/11/13/431

That used the generic PROT_NONE infrastructure and compared, on fault,
the page protection bits against the vma->vm_page_prot bits?

So the objection to that approach was the vma-> dereference in
pte_numa() ?

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