linux-kernel - Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for _PAGE

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Message-ID: <20140408173031.GS10526@twins.programming.kicks-ass.net>
Date:	Tue, 8 Apr 2014 19:30:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Linux-X86 <x86@...nel.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Noonan <steven@...inklabs.net>,
	Rik van Riel <riel@...hat.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for
 _PAGE_NUMA v2

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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