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Date: Thu, 18 Oct 2012 15:05:02 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Will Deacon <will.deacon@arm.com>
Cc: David Miller <davem@davemloft.net>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
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        "cmetcalf@tilera.com" <cmetcalf@tilera.com>,
        Steve Capper <Steve.Capper@arm.com>
Subject: Re: [PATCH v2] mm: thp: Set the accessed flag for old pages on
 access fault.
Message-Id: <20121018150502.3dee7899.akpm@linux-foundation.org>
In-Reply-To: <20121017155401.GJ5973@mudshark.cambridge.arm.com>
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On Wed, 17 Oct 2012 16:54:02 +0100
Will Deacon <will.deacon@arm.com> wrote:

> On x86 memory accesses to pages without the ACCESSED flag set result in the
> ACCESSED flag being set automatically. With the ARM architecture a page access
> fault is raised instead (and it will continue to be raised until the ACCESSED
> flag is set for the appropriate PTE/PMD).
> 
> For normal memory pages, handle_pte_fault will call pte_mkyoung (effectively
> setting the ACCESSED flag). For transparent huge pages, pmd_mkyoung will only
> be called for a write fault.
> 
> This patch ensures that faults on transparent hugepages which do not result
> in a CoW update the access flags for the faulting pmd.

Confused.  Where is the arm implementation of update_mmu_cache_pmd()?