Massive memory/process size increases in recent java releases

FULL PRODUCT VERSION :
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Server VM (build 16.3-b01, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Linux drill.jpl.nasa.gov 2.6.18-194.11.1.el5PAE #1 SMP Tue Jul 27 06:02:35 EDT 2010 i686 i686 i386 GNU/Linux


A DESCRIPTION OF THE PROBLEM :
When we went from build 17 to build 20, the size of all our Java processes and their associated heaps DOUBLED. Build 23 does not fix the problem.

jconsole heap size in build 17 was 300MB.
jconsole heap size in build 20 is 600MB.
jconsole heap size in build 23 could not be measured because the darned thing won't even connect to jconsole.

process size in build 17 was 500MB.
process size in build 20 is 1.1GB.

This is the same code, doing the same thing, all compiled with build 20.

This is absolutely killing us. What happened? Did the garbage collection change in some way?



REPRODUCIBILITY :
This bug can be reproduced always.