Turning off sysfs support can save a substantial amount of memory in some setups. One big downside is that it breaks the normal boot process because the kernel can no longer map a symbolic device name to the internal device numbers.
Thus, you will need to pass a numeric device number in hex. For example, to boot off /dev/hda1, which has major number 3 and minor 1, you'll need to append a root= option like this:
/boot/vmlinuz root=0x0301 ro