XLOG_TOTAL_REC_SHIFT
min_t(int, (log)->l_logsize >> 3, BBTOB(XLOG_TOTAL_REC_SHIFT(log)) << 4)
num_scan_bblks = XLOG_TOTAL_REC_SHIFT(log);
max_distance = XLOG_TOTAL_REC_SHIFT(log);
num_scan_bblks = min_t(int, log_bbnum, XLOG_TOTAL_REC_SHIFT(log));