I found a couple of issues with reserve_mem:

- If we try and mem_reserve something of zero length, everything
  reserved after it would get ignored. This is because early_reserve_mem
  sees a zero length as a terminator.
- The code rounded the top down instead of up.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>