PG_DIRECT_MAP_2G
update_page_count(PG_DIRECT_MAP_2G, pages);
update_page_count(PG_DIRECT_MAP_2G, -1);
atomic_long_read(&direct_pages_count[PG_DIRECT_MAP_2G]) << 21);
update_page_count(PG_DIRECT_MAP_2G, add ? pages : -pages);