On 10/26/2012 03:51 AM, Johannes Weiner wrote:

On Thu, Oct 25, 2012 at 05:44:31PM +0100, Will Deacon wrote:

quoted

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 <redacted>
Cc: Kirill A. Shutemov <redacted>
Cc: Andrea Arcangeli <redacted>
Signed-off-by: Will Deacon <redacted>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

quoted

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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