mm/writeback: correct dirty page calculation for highmem

mm/writeback: correct dirty page calculation for highmem

ZONE_MOVABLE could be treated as highmem so we need to consider it for
accurate calculation of dirty pages.  And, in following patches,
ZONE_CMA will be introduced and it can be treated as highmem, too.  So,
instead of manually adding stat of ZONE_MOVABLE, looping all zones and
check whether the zone is highmem or not and add stat of the zone which
can be treated as highmem.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>