[plt-scheme] minimizing garbage collection time

I'm noticing that my program spends a large portion of its time
collecting garbage.  What are some ways to deal with this (other than
creating less garbage, which is one thing that led to my previous post
about `map' reusing cons cells)?  My impression of the 3m collector is
that it (potentially) uses less memory, but isn't any faster-- is that
correct?  (Is there more documentation about using 3m than what's in
src/README?)  Is there a way to increase memory size, or otherwise
lower the frequency of garbage collection?

--dougo at place.org