[U-Boot-Users] reserving RAM

Hi, I am using a freescale eval board with 256M DDR, and want to bootup the Linux kernel with only a part of this memory, I tried setting the memsize env variable to (equivalent of this value in hex), no use. then i appened bootargs with "boot=128m", and saveenv. Linux still boots without the appended bootargs, any ideas what is causing this?

thanks