Re: [PATCH v3] mm: thp: Set the accessed flag for old pages on accessfault.

[Ni zhan Chen]

On 10/26/2012 05:34 PM, Will Deacon wrote:
> On Fri, Oct 26, 2012 at 07:19:55AM +0100, Ni zhan Chen wrote:
> > On 10/26/2012 12:44 AM, 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.
> > Could you write changlog?
> >From v2? I included something below my SoB. The code should do exactly the
> same as before, it's just rebased onto next so that I can play nicely with
> Peter's patches.
>
> > > Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> > > Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> > > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > > Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> > > ---
> > >
> > > 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.
> > >
> > > Cheers,
> > >
> > > Will
> > Could you explain why you not call pmd_trans_huge_lock to confirm the
> > pmd is splitting or stable as Andrea point out?
> The way handle_mm_fault is now structured after the numa changes means that
> we only enter the huge pmd page aging code if the entry wasn't splitting

Why you call it huge pmd page *aging* code?

Regards,
Chen

> before taking the lock, so it seemed a bit gratuitous to jump through those
> hoops again in pmd_trans_huge_lock.
>
> Will

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