TOTAL_PG_BD_PER_PAGE
#define USABLE_PG_BD_PER_PAGE (TOTAL_PG_BD_PER_PAGE - 1)
#define MAX_PG_BD_AVAIL (MAX_PG_PAGES * TOTAL_PG_BD_PER_PAGE)
#define TOTAL_PG_BD_ALLOC (TOTAL_PG_BD_PER_PAGE * sc->pg_pages)