Memory NEVER freed!

[Jean-Eric Cuendet]

Hi,
I have a problem. One of my program allocate a LOT of small pieces of memory with new/delete.
When freed, the RSS of my prog doesnt change!
I *THINK* that the memory is freed since if I alloc again the same space, the RSS doesnt change. But the RSS *NEVER* come back to the level it was before the allocation.
Ex: 
Begin: RSS=10Mb
Alloc 50Mb => RSS=60Mb
Free 30MB=>RSS=60Mb
Free remaining 20Mb=>RSS=60Mb
!!!!
Alloc 30Mb=>RSS=60Mb
Alloc 30Mb=>RSS=70Mb
Free 60Mb=>RSS=70Mb
 
Why?
Is there a way to tell my prog to release the not used pages?
Is there a compact memory method?
 
Thanks for any help.
-jec
 
PS: Im not in the list so please CC me. Thanks.