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

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Message-ID: <20140408181606.GL23983@moon>
Date:	Tue, 8 Apr 2014 22:16:06 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mel Gorman <mgorman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Linux-X86 <x86@...nel.org>,
	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>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for
 _PAGE_NUMA v2

On Tue, Apr 08, 2014 at 07:30:31PM +0200, Peter Zijlstra wrote:
> 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() ?

Peter, I somehow missing, with this patch would it be possible to
get rid of ugly macros in 2 level pages like we have now? (I've
dropped off softdirty support for non x86-64 now [patches are
flying around]) but still there are a few remains which make
Linus unhappy.

static __always_inline pgoff_t pte_to_pgoff(pte_t pte)
{
	return (pgoff_t)
		(pte_bitop(pte.pte_low, PTE_FILE_SHIFT1, PTE_FILE_MASK1,  0)		    +
		 pte_bitop(pte.pte_low, PTE_FILE_SHIFT2, PTE_FILE_MASK2,  PTE_FILE_LSHIFT2) +
		 pte_bitop(pte.pte_low, PTE_FILE_SHIFT3,           -1UL,  PTE_FILE_LSHIFT3));
}
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