From: Martin Schwidefsky <schwidefsky@de.ibm.com>

this is another s/390 related mm patch. It introduces the concept of
physical dirty and referenced bits into the common mm code. I always
had the nagging feeling that the pte functions for setting/clearing
the dirty and referenced bits are not appropriate for s/390. It works
but it is a bit of a hack. 
After the wake of rmap it is now possible to put a much better solution
into place. The idea is simple: since there are not dirty/referenced
bits in the pte make these function nops on s/390 and add operations
on the physical page to the appropriate places. For the referenced bit
this is the page_referenced() function. For the dirty bit there are
two relevant spots: in page_remove_rmap after the last user of the
page removed its reverse mapping and in try_to_unmap after the last
user was unmapped. There are two new functions to accomplish this:

 * page_test_and_clear_dirty: Test and clear the dirty bit of a
   physical page. This function is analog to ptep_test_and_clear_dirty
   but gets a struct page as argument instead of a pte_t pointer.

 * page_test_and_clear_young: Test and clear the referenced bit
   of a physical page. This function is analog to ptep_test_and_clear_young
   but gets a struct page as argument instead of a pte_t pointer.

Its pretty straightforward and with it the s/390 mm makes much more
sense. You'll need the tls flush optimization patch for the patch.
Comments ?