linux-kernel - Re: [PATCH v3] mm: thp: Set the accessed flag for old pages on access fault.

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Date:	Fri, 26 Oct 2012 11:07:58 +0800
From:	Ni zhan Chen <nizhan.chen@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Will Deacon <will.deacon@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	mhocko@...e.cz, peterz@...radead.org, akpm@...ux-foundation.org,
	Chris Metcalf <cmetcalf@...era.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v3] mm: thp: Set the accessed flag for old pages on access
 fault.

On 10/26/2012 03:51 AM, Johannes Weiner wrote:
> On Thu, Oct 25, 2012 at 05:44:31PM +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: Chris Metcalf <cmetcalf@...era.com>
>> Cc: Kirill A. Shutemov <kirill@...temov.name>
>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>> Signed-off-by: Will Deacon <will.deacon@....com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
>
>> Ok chaps, I rebased this thing onto today's next (which basically
>> necessitated a rewrite) so I've reluctantly dropped my acks and kindly
>> ask if you could eyeball the new code, especially where the locking is
>> concerned. In the numa code (do_huge_pmd_prot_none), Peter checks again
>> that the page is not splitting, but I can't see why that is required.
> I don't either.  If the thing was splitting when the fault happened,
> that path is not taken.  And the locked pmd_same() check should rule
> out splitting setting in after testing pmd_trans_huge_splitting().

Why I can't find function pmd_trans_huge_splitting() you mentioned in 
latest mainline codes and linux-next?

>
> Peter?
>
> --
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