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

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Message-ID: <53441E19.8090004@zytor.com>
Date:	Tue, 08 Apr 2014 09:04:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Mel Gorman <mgorman@...e.de>, 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>,
	Peter Zijlstra <peterz@...radead.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 04/08/2014 08:22 AM, Linus Torvalds wrote:
> On Tue, Apr 8, 2014 at 7:40 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> David, is your patchset going to be pushed in this merge window as expected?
> 
> Apparently aiming for 3.16 right now.
> 
>> That being said, these bits are precious, and if this ends up being a
>> case where "only Xen needs another bit" once again then Xen should
>> expect to get kicked to the curb at a moment's notice.
> 
> Quite frankly, I don't think it's a Xen-only issue. The code was hard
> to figure out even without the Xen issues. For example, nobody ever
> explained to me why it
> 
>  (a) could be the same as PROTNONE on x86
>  (b) could not be the same as PROTNONE in general
> 
> I think the best explanation for it so far was from the little voices
> in my head that sang "It's a kind of Magic", and that isn't even
> remotely the best song by Queen.
> 

Yes, I was hoping that the timing would work out so we could evict bit
10 (which *is* a Xen-only issue) and then reuse it.  I don't think the
NUMA bit is Xen-only.

	-hpa


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