linux-kernel - Re: [BISECTED] Linux 3.12.7 introduces page map handling regression

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Message-ID: <52E01064.9090905@redhat.com>
Date:	Wed, 22 Jan 2014 13:39:32 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Steven Noonan <steven@...inklabs.net>,
	Linux Kernel mailing List <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Mel Gorman <mgorman@...e.de>,
	Alex Thorlton <athorlton@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [BISECTED] Linux 3.12.7 introduces page map handling regression

On 01/22/2014 01:24 PM, Linus Torvalds wrote:
> On Wed, Jan 22, 2014 at 10:07 AM, Rik van Riel <riel@...hat.com> wrote:
>>
>> The difference between a numa pte and a protnone pte is
>> the VMA permissions.
>
> If that is indeed the only difference, then we should damn well get
> rid of that f*cking stupid _PAGE_NUMA name entirely.
>
> It's misleading crap. Really. Just do a quick grep for that bit, and
> you see just *how* confused people are about it:
>
>     #define _PAGE_NUMA _PAGE_PROTNONE
>     ...
>          if ((pte_flags(a) & (_PAGE_PROTNONE | _PAGE_NUMA)) &
>
> think about it. Just *THINK* about how broken that code is. The whole
> thing is a disaster. _PAGE_NUMA must die. It's shit.

The reason things are this way is that we were
not sure whether we can indeed use _PAGE_PROTNONE
for NUMA balancing on all architectures.

If we are sure that _PAGE_PROTNONE can be used
everywhere, I agree we should get rid of the whole
_PAGE_NUMA naming, and replace that ambiguous
code with some comments and documentation instead.

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