pagewalk: only split huge pages when necessary

Right now, if a mm_walk has either ->pte_entry or ->pmd_entry set, it will
unconditionally split any transparent huge pages it runs in to.  In
practice, that means that anyone doing a

	cat /proc/$pid/smaps

will unconditionally break down every huge page in the process and depend
on khugepaged to re-collapse it later.  This is fairly suboptimal.

This patch changes that behavior.  It teaches each ->pmd_entry handler
(there are five) that they must break down the THPs themselves.  Also, the
_generic_ code will never break down a THP unless a ->pte_entry handler is
actually set.

This means that the ->pmd_entry handlers can now choose to deal with THPs
without breaking them down.

[[email protected]: coding-style fixes]
Signed-off-by: Dave Hansen <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Acked-by: David Rientjes <[email protected]>
Reviewed-by: Eric B Munson <[email protected]>
Tested-by: Eric B Munson <[email protected]>
Cc: Michael J Wolf <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Matt Mackall <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions