DB2 memory usage help

Im runnign various versions of DB2 on various UNIX platforms
(Solaris / AIX).

DB2 is generally eating up about 30% of memory on these systems (4Gb
of RAM, which equates to over a gig). i want to limit DB2s memory
usage to a couple of hundred meg in total for the entire application,
but cannot seem to find out how to do this.

When i check the instance memory usage with db2mtrk, it says its only
using a few Megs. I cannot find out how to limit the whole operation
to something like 250M or 500M or there abouts.

Can anyone help?