Why does the Java VM process eat up more RAM then specified in -Xmx parameter?

Posted by evilpenguin on Server Fault See other posts from Server Fault or by evilpenguin
Published on 2010-05-12T09:57:04Z Indexed on 2010/05/12 10:04 UTC
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Filed under:

java

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linux

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centos

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java-opts

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memory

I have multiple servers running CentOS 5.4 and only one application running on Java VM. I've configured the Java VM with the following arguments:

java -Xmx4500M -server -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:NewSize=1024m  -Djava.net.preferIPv4Stack=true -Dcom.sun.management.jmxremote=true

The machines I'm running the VM on has 6 GB RAM and no other applications running. After a while, the java process starts to hit the swap space really hard, I get this info out of the top command:

7658 root      25   0 11.7g 3.9g 4796 S 39.4 67.3 543:54.17 java

On the other hand, if I connect via JConsole, it reports the Java VM has 2.6 GB used, 4.6 GB commited and 4.6 Gb max.

java -version returns:

java version "1.6.0_17"
Java(TM) SE Runtime Environment (build 1.6.0_17-b04)
Java HotSpot(TM) 64-Bit Server VM (build 14.3-b01, mixed mode)

Why is the Java VM expanding so much past it's allocated heap size? And where does that memory go, if it's not reported in JConsole?

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