create ramdisk filesystem

[Tom Greaser]

ive been doing some looking 
and I see under my /dev that i have some 
ramdisk devices already setup.. 
 
but after mkfs + mounting one device (ram9) 
it only 16M .. how can i  create 
a ram disk of my own size requirements ? 
 
have tried 
ramsize /dev/ram9 500000 
 
rdev -r /dev/ram9 500000 
both .. no luck!! 
 
at kernel boot up i can use grub to pass 
ramdisk_size=500000 and that works!!!!! 
 
Thanks