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

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Message-Id: <20121002150104.da57fa94.akpm@linux-foundation.org>
Date:	Tue, 2 Oct 2012 15:01:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Will Deacon <will.deacon@....com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, mhocko@...e.cz, kirill@...temov.name,
	Andrea Arcangeli <aarcange@...hat.com>,
	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,  2 Oct 2012 17:59:11 +0100
Will Deacon <will.deacon@....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.

Alas, the code you're altering has changed so much in linux-next that I
am reluctant to force this fix in there myself.  Can you please
redo/retest/resend?  You can do that on 3.7-rc1 if you like, then we
can feed this into -rc2.

> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3524,7 +3524,8 @@ retry:
>  
>  		barrier();
>  		if (pmd_trans_huge(orig_pmd)) {
> -			if (flags & FAULT_FLAG_WRITE &&
> +			int dirty = flags & FAULT_FLAG_WRITE;

`flags' is `unsigned int', so making `dirty' match that is nicer.


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