What does this Max value stands for in J VisualVm?

Question

Hi I can not find a document?

Our vm options is like this .

-D[Server:jbossvat1_server01]
-XX:PermSize=256m
-XX:MaxPermSize=256m
-Xms3072m
-Xmx3072m
-XX:+UseG1GC
-Djboss.modules.policy-permissions=true
-Djava.awt.headless=true
-Dorg.apache.catalina.connector.URI_ENCODING=UTF-8
-Djboss.modules.system.pkgs=org.jboss.byteman
-Djboss.home.dir=/u01/jboss/jboss-eap-6.3
-Djava.net.preferIPv4Stack=true
-Dfile.encoding=UTF-8
-Djboss.server.log.dir=/u01/jboss/jboss-eap-6.3/domain/servers/jboss1_server01/log
-Djboss.server.temp.dir=/u01/jboss/jboss-eap-6.3/domain/servers/jboss1_server01/tmp
-Djboss.server.data.dir=/u01/jboss/jboss-eap-6.3/domain/servers/jboss1_server01/data
-Dlogging.configuration=file:/u01/jboss/jboss-eap-6.3/domain/servers/jboss1_server01/data/logging.properties

My original problem is memory allocation from OS side is a way larger than xmx side. It goes 5.1 gb in one jboss instance after 9 hours of load.

Just see the Max value on jvisualvm and wonder what it is? And It is almost doubled of my max heap value? Why is this?

Could you please help me?

Answer 1

Max means -Xmx value that I set + -XX:+UseG1GC garbace collector puts an overhead to maximum heap size.

So please be careful using G1 garbage collector. It can give you headache.