[CentOS] how to change fsize to unlimited..

Dear centos experts,
    I am wondering is there a way for me to change ulimit fsize  
parameter? I am trying to change it to unlimited, so
I added the following line to /etc/security/limits.conf
  - - fsize  -1
but it does not work, and a reboot will reset the content of  
limits.conf.

thanks,
yan