mm: use zone->present_pages instead of zone->managed_pages where appropriate

mm: use zone->present_pages instead of zone->managed_pages where appropriate

Now we have zone->managed_pages for "pages managed by the buddy system
in the zone", so replace zone->present_pages with zone->managed_pages if
what the user really wants is number of allocatable pages.

Signed-off-by: Jiang Liu <[email protected]>
Cc: Wen Congyang <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Jiang Liu <[email protected]>
Cc: Maciej Rutecki <[email protected]>
Cc: Chris Clayton <[email protected]>
Cc: "Rafael J . Wysocki" <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Jianguo Wu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>