bd = allocGroup(req_blocks);
dbl_link_onto(bd, &g0->large_objects);
g0->n_large_blocks += bd->blocks; // might be larger than req_blocks
bd = allocGroup(req_blocks);
dbl_link_onto(bd, &g0->large_objects);
g0->n_large_blocks += bd->blocks; // might be larger than req_blocks