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

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Date:	Mon, 22 Oct 2012 11:35:03 +0100
From:	Will Deacon <will.deacon@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	"kirill@...temov.name" <kirill@...temov.name>,
	"aarcange@...hat.com" <aarcange@...hat.com>,
	"cmetcalf@...era.com" <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 Fri, Oct 19, 2012 at 07:49:55PM +0100, Andrew Morton wrote:
> On Fri, 19 Oct 2012 10:10:16 +0100
> Will Deacon <will.deacon@....com> wrote:
> 
> > On Thu, Oct 18, 2012 at 11:05:02PM +0100, Andrew Morton wrote:
> > > On Wed, 17 Oct 2012 16:54:02 +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.
> > > 
> > > Confused.  Where is the arm implementation of update_mmu_cache_pmd()?
> > 
> > Right at the end of this patch, which was posted to the ARM list yesterday:
> > 
> >   http://lists.infradead.org/pipermail/linux-arm-kernel/2012-October/126387.html
> 
> I received and then merged a patch which won't compile!

Eek, that certainly wasn't intentional and it's compiling fine for me on
-rc1 and -rc2 for both ARM (no THP) and x86 (with and without THP).

Please can you send the build failure?

> Ho hum.  I'll drop
> mm-thp-set-the-accessed-flag-for-old-pages-on-access-fault.patch and
> shall assume that you'll sort things out at the appropriate time.

Happy to sort it out once I work out what's going wrong!

Cheers,

Will
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