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Date: Tue, 13 Nov 2012 14:51:08 +0100
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 06/19] mm: numa: teach gup_fast about pmd_numa
Message-ID: <20121113135107.GC17782@gmail.com>
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To: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, Hugh Dickins <hughd@google.com>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>


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

> On Tue, Nov 13, 2012 at 11:07:36AM +0100, Ingo Molnar wrote:
> > 
> > * Mel Gorman <mgorman@suse.de> wrote:
> > 
> > > From: Andrea Arcangeli <aarcange@redhat.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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