mm: factor out common parts between MADV_COLD and MADV_PAGEOUT

mm: factor out common parts between MADV_COLD and MADV_PAGEOUT

There are many common parts between MADV_COLD and MADV_PAGEOUT.
This patch factor them out to save code duplication.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Suggested-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Chris Zankel <[email protected]>
Cc: Daniel Colascione <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Joel Fernandes (Google) <[email protected]>
Cc: kbuild test robot <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Oleksandr Natalenko <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Sonny Rao <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Tim Murray <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>