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

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Message-ID: <5343C1F6.4090600@citrix.com>
Date:	Tue, 8 Apr 2014 10:31:34 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Mel Gorman <mgorman@...e.de>,
	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 07/04/14 20:36, 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?

Not yet.

A last minute regression with mapping of I/O regions from userspace was
found so I had to drop the series from 3.15.  It should be back for 3.16.

> 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).

Xen uses it for all I/O mappings, both kernel and for userspace.

David

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