metaslab_class_create
spa->spa_normal_class = metaslab_class_create(spa, zfs_metaslab_ops);
spa->spa_log_class = metaslab_class_create(spa, zfs_metaslab_ops);
spa->spa_special_class = metaslab_class_create(spa, zfs_metaslab_ops);
spa->spa_dedup_class = metaslab_class_create(spa, zfs_metaslab_ops);
metaslab_class_t *metaslab_class_create(spa_t *, metaslab_ops_t *);