RADIX_TREE_MAP_SHIFT
#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
howmany(sizeof(long) * NBBY, RADIX_TREE_MAP_SHIFT)
unsigned long mask = RADIX_TREE_MAP_MASK << (RADIX_TREE_MAP_SHIFT * height);
unsigned long step = 1UL << (RADIX_TREE_MAP_SHIFT * height);
return ((1UL << (root->height * RADIX_TREE_MAP_SHIFT)) - 1UL);
return (id >> (RADIX_TREE_MAP_SHIFT * height)) & RADIX_TREE_MAP_MASK;