Oracle suggests to use extends 160K. Furthermore you might want to set the limit to
create tablespace service_name datafile
'/ora8/m02/oradata/ora8/service_name01.dbf' size 50m autoextend on
next 640k maxsize 2147450880 extent management local uniform size
160K;
Furthermore make sure that the extend size (next XXX) is a multiple of the uniform size. And the maxsize should bring you on the safe side with the Linux 2GB oracle limitation.
