ddt_stat_add
ddt_stat_add(&ddh_total.ddh_stat[highbit64(refcnt) - 1],
ddt_stat_add(&ddh->ddh_stat[bucket], &dds, neg);
ddt_stat_add(&dst->ddh_stat[h], &src->ddh_stat[h], 0);
ddt_stat_add(dds, &ddh->ddh_stat[h], 0);
extern void ddt_stat_add(ddt_stat_t *dst, const ddt_stat_t *src, uint64_t neg);