linux-kernel - Re: [PATCH 06/19] mm: numa: teach gup_fast about pmd

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Date:	Tue, 13 Nov 2012 14:51:08 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	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 06/19] mm: numa: teach gup_fast about pmd_numa


* Mel Gorman <mgorman@...e.de> wrote:

> On Tue, Nov 13, 2012 at 11:07:36AM +0100, Ingo Molnar wrote:
> > 
> > * Mel Gorman <mgorman@...e.de> wrote:
> > 
> > > From: Andrea Arcangeli <aarcange@...hat.com>
> > > 
> > > When scanning pmds, the pmd may be of numa type (_PAGE_PRESENT not set),
> > > however the pte might be present. Therefore, gup_pmd_range() must return
> > > 0 in this case to avoid losing a NUMA hinting page fault during gup_fast.
> > > 
> > > Note: gup_fast will skip over non present ptes (like numa 
> > > types), so no explicit check is needed for the pte_numa case. 
> > > [...]
> > 
> > So, why not fix all architectures that choose to expose 
> > pte_numa() and pmd_numa() methods - via the patch below?
> > 
> 
> I'll pick it up. Thanks.

FYI, before you do too much restructuring work, that patch is 
already part of tip:numa/core, I'll push out our updated version 
of the tree later today.

Thanks,

	Ingo
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