On my machine, rdoc continues to consume memory until the system becomes
unusable.  I have to kill the process before it finishes. Since it seems to
generate all its files at the end, I end up with no documentation generated.
What can I do, short of buying more memory?

I'm using ruby 1.8.2 (2004-12-25) [i686-linux].  

Here are snapshots from top(1) and vmstat(1) as the process size grows:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
32113 joshp     25   0  7464 5408 2192 R 87.1  1.7   0:03.80 rdoc
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 0  0 160084 204368   2060  30892    3    2    12    15   42     1 20 54 25  0

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
32126 joshp     25   0  104m 102m 2192 R 86.1 32.5   6:08.95 rdoc               procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 1  0 152100   8364  22616  64468    3    2    12    15   41    62 20 54 25  0

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
32126 joshp     25   0  200m 197m 2192 R 83.1 63.0  13:15.79 rdoc               procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 1  0 176068   1564   1932  30688    3    2    12    15   42     1 20 54 25  0
-- 
Josh Purinton