BITS_PER_PAGE      18 include/linux/pid_namespace.h #define BITS_PER_PAGE_MASK	(BITS_PER_PAGE-1)
BITS_PER_PAGE      19 include/linux/pid_namespace.h #define PIDMAP_ENTRIES		((PID_MAX_LIMIT+BITS_PER_PAGE-1)/BITS_PER_PAGE)