BM_RTREE_LEVEL_SHIFT
#define BM_RTREE_LEVEL_MASK ((1UL << BM_RTREE_LEVEL_SHIFT) - 1)
block_nr >>= BM_RTREE_LEVEL_SHIFT;
index = block_nr >> ((i - 1) * BM_RTREE_LEVEL_SHIFT);
index = block_nr >> ((i - 1) * BM_RTREE_LEVEL_SHIFT);