linux-kernel - Re: [PATCH 08/19] mm: numa: Create basic numa page hinting infrastructure

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Message-ID: <50995DD2.8000200@redhat.com>
Date:	Tue, 06 Nov 2012 13:58:26 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/19] mm: numa: Create basic numa page hinting infrastructure

On 11/06/2012 04:14 AM, Mel Gorman wrote:
> Note: This patch started as "mm/mpol: Create special PROT_NONE
> 	infrastructure" and preserves the basic idea but steals *very*
> 	heavily from "autonuma: numa hinting page faults entry points" for
> 	the actual fault handlers without the migration parts.	The end
> 	result is barely recognisable as either patch so all Signed-off
> 	and Reviewed-bys are dropped. If Peter, Ingo and Andrea are ok with
> 	this version, I will re-add the signed-offs-by to reflect the history.
>
> In order to facilitate a lazy -- fault driven -- migration of pages, create
> a special transient PAGE_NUMA variant, we can then use the 'spurious'
> protection faults to drive our migrations from.
>
> Pages that already had an effective PROT_NONE mapping will not be detected

The patch itself is good, but the changelog needs a little
fix. While you are defining _PAGE_NUMA to _PAGE_PROTNONE on
x86, this may be different on other architectures.

Therefore, the changelog should refer to PAGE_NUMA, not
PROT_NONE.

> to generate these 'spurious' faults for the simple reason that we cannot
> distinguish them on their protection bits, see pte_numa(). This isn't
> a problem since PROT_NONE (and possible PROT_WRITE with dirty tracking)
> aren't used or are rare enough for us to not care about their placement.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Other than the changelog ...

Reviewed-by: Rik van Riel <riel@...hat.com>
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