prios_per_bucket
DIV_ROUND_UP((size_t) (ca)->sb.nbuckets, prios_per_bucket(ca))
struct bucket_disk *end = d + prios_per_bucket(ca);
for (b = ca->buckets + i * prios_per_bucket(ca);
struct bucket_disk *d = p->data + prios_per_bucket(ca), *end = d;