mdconfig unable to allocate memory

Hello,

I'm just fiddling with mdconfig and trying to create a rather
large memory disk, but I can't understand why it's failing.

this fails:
cluestick# mdconfig -a -t malloc -o reserve -s 1g
mdconfig: ioctl(/dev/mdctl): Cannot allocate memory


But given these variables, shouldn't it work..?
cluestick# limits
Resource limits (current):
  cputime          infinity secs
  filesize         infinity kb
  datasize          2097152 kb
  stacksize         2097152 kb
  coredumpsize     infinity kb
  memoryuse        infinity kb
  memorylocked     infinity kb
  maxprocesses         5547
  openfiles           11095
  sbsize           infinity bytes
  vmemoryuse       infinity kb
uestick# egrep "(MAXDSIZ|MAXSSIZ|DFLDSIZ)" /usr/src/sys/i386/conf/CLUESTICK
options         MAXDSIZ=(2048UL*1024*1024)
options         MAXSSIZ=(2048UL*1024*1024)
options         DFLDSIZ=(1024UL*1024*1024)
cluestick# sysctl -a | egrep "hw.(phys|user)mem"
hw.physmem: 4222963712
hw.usermem: 4171063296
%./test & && ps u | grep test
[7] 648
chris   645  0.0  0.0 1050788 1612  p2  SL   10:14AM   0:00.01 ./test


What have I missed? Is mdconfig simply not designed to cope with
memory disks this large? I was eventually hoping to create
around 2GB. As you can see, ./test is managing to malloc(1024*1024*1024)
and then sleep, although it doesn't touch any of it.

Cheers for any advice,

-- 
Chris