zone_reclaimable_pages
extern unsigned long zone_reclaimable_pages(struct zone *zone);
available = zone_reclaimable_pages(zone) / order;
available = reclaimable = zone_reclaimable_pages(zone);
reclaimable += zone_reclaimable_pages(zone);
if (!zone_reclaimable_pages(zone) && zone_page_state_snapshot(zone, NR_FREE_PAGES))