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

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Message-ID: <20140408170310.GO7292@suse.de>
Date:	Tue, 8 Apr 2014 18:03:11 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"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>,
	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 Tue, Apr 08, 2014 at 05:46:52PM +0100, Mel Gorman wrote:
> On Tue, Apr 08, 2014 at 08:22:15AM -0700, 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
> 
> This series exists in response to your comment
> 
> 	I fundamentally think that it was a horrible horrible disaster to
> 	make _PAGE_NUMA alias onto _PAGE_PROTNONE.
> 
> As long as _PAGE_NUMA aliases to _PAGE_PROTNONE on x86 then the core has to
> play games to take that into account and the code will be "hard to figure
> out even without the Xen issues".

Is what you want for _PAGE_NUMA to disappear from arch/x86 and instead
use _PAGE_PROTNONE with comments explaining why and leave the core as it
is?

-- 
Mel Gorman
SUSE Labs
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