Make zone_pagecache_reclaimable() return ulong rather than long. Negative
values are meainingless here and all zone_pagecache_reclaimable() callers
turn its retrun value into ulong anyway.
Cc: Vladimir Davydov <vdavydov@parallels.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Mel Gorman <mgorman@suse.de> Cc: Alexandru Moise <00moses.alexander00@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>