linux-kernel - Re: [PATCH 2/3] x86: Define _PAGE_NUMA with unused physical address bits PMD and PTE levels

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Date:	Mon, 07 Apr 2014 12:42:40 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Mel Gorman <mgorman@...e.de>,
	David Vrabel <david.vrabel@...rix.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Noonan <steven@...inklabs.net>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux-MM <linux-mm@...ck.org>, Linux-X86 <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH 2/3] x86: Define _PAGE_NUMA with unused physical address
 bits PMD and PTE levels

On 04/07/2014 12:36 PM, Cyrill Gorcunov wrote:
> On Mon, Apr 07, 2014 at 12:27:10PM -0700, H. Peter Anvin wrote:
>> On 04/07/2014 11:28 AM, Mel Gorman wrote:
>>>
>>> I had considered the soft-dirty tracking usage of the same bit. I thought I'd
>>> be able to swizzle around it or a further worst case of having soft-dirty and
>>> automatic NUMA balancing mutually exclusive. Unfortunately upon examination
>>> it's not obvious how to have both of them share a bit and I suspect any
>>> attempt to will break CRIU.  In my current tree, NUMA_BALANCING cannot be
>>> set if MEM_SOFT_DIRTY which is not particularly satisfactory. Next on the
>>> list is examining if _PAGE_BIT_IOMAP can be used.
>>
>> Didn't we smoke the last user of _PAGE_BIT_IOMAP?
> 
> Seems so, at least for non-kernel pages (not considering this bit references in
> xen code, which i simply don't know but i guess it's used for kernel pages only).
> 

David Vrabel has a patchset which I presumed would be pulled through the
Xen tree this merge window:

[PATCHv5 0/8] x86/xen: fixes for mapping high MMIO regions (and remove
_PAGE_IOMAP)

That frees up this bit.

	-hpa

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