linux-kernel - Re: [PATCH v2] mm: thp: Set the accessed flag for old pages on access fault.

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Date:	Tue, 2 Oct 2012 19:46:24 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Will Deacon <will.deacon@....com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, akpm@...ux-foundation.org,
	mhocko@...e.cz, kirill@...temov.name,
	Chris Metcalf <cmetcalf@...era.com>,
	Steve Capper <steve.capper@....com>
Subject: Re: [PATCH v2] mm: thp: Set the accessed flag for old pages on
 access fault.

On Tue, Oct 02, 2012 at 05:59:11PM +0100, Will Deacon 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.
> 
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Chris Metcalf <cmetcalf@...era.com>
> Signed-off-by: Steve Capper <steve.capper@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
> 
> v2: - Use pmd_trans_huge_lock to guard against splitting pmds
>     - Propogate dirty (write) flag to low-level pmd modifier
> 
>  include/linux/huge_mm.h |    2 ++
>  mm/huge_memory.c        |    8 ++++++++
>  mm/memory.c             |    9 ++++++++-
>  3 files changed, 18 insertions(+), 1 deletions(-)

Reviewed-by: Andrea Arcangeli <aarcange@...hat.com>
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