why try_attach every list entry in __register_sysctl_paths of sysctl.c#kernel code

Question

i am reading the sysctl code about linux kernel 3.3.8 in function __register_sysctl_paths of sysctl.c why call try_attach on every entry of the list, what is the meaning of 'improvement' on "/* see if attaching q to p would be an improvement */ static void try_attach(struct ctl_table_header *p, struct ctl_table_header *q)"?

    for (set = header->set; set; set = set->parent) {
        struct ctl_table_header *p;
        list_for_each_entry(p, &set->list, ctl_entry) {
            if (p->unregistering)
                continue;
            try_attach(p, header);
        }
    }

i am confused by these statements.