java on AIX6.1

[cpu533]

Hi,

We have some java program running on our AIX 6.1 server.
I am not familiar with JAVA. Basically this java application has the below setting. -Xms512m -Xmx2048m -XX:MaxPermSize=512m
I am using svmon to capture the actual memory been used by this java application.
Please see below capture.
initial capture:
-------------------------------------------------------------------------------
Pid Command Inuse Pin Pgsp Virtual 64-bit Mthrd 16MB
25755686 java 107064 8305 0 104162 Y Y N

107064*4K = 418 M

in the middle of the day:
-------------------------------------------------------------------------------
Pid Command Inuse Pin Pgsp Virtual 64-bit Mthrd 16MB
25755686 java 351450 8402 0 351360 Y Y N

351450 * 4K = 1372 M

with heavy data load;
-------------------------------------------------------------------------------
Pid Command Inuse Pin Pgsp Virtual 64-bit Mthrd 16MB
25755686 java 652784 8427 4022 649612 Y Y N

652784 * 4K = 2549 M

So my question is why this java application used 2.5G memory as the xmx only set to 2048M?

THanks,
Denny