MAX_IO_TYPE
struct f2fs_iostat_latency iostat_lat[MAX_IO_TYPE][NR_PAGE_TYPE];
for (idx = 0; idx < MAX_IO_TYPE; idx++) {
unsigned long sum_lat[MAX_IO_TYPE][NR_PAGE_TYPE]; /* sum of io latencies */
unsigned long peak_lat[MAX_IO_TYPE][NR_PAGE_TYPE]; /* peak io latency */
unsigned int bio_cnt[MAX_IO_TYPE][NR_PAGE_TYPE]; /* bio count */