We have production Tomcat (6.0.18) server which runs with the following settings:
-server -Xms7000M -Xmx7000M -Xss128k -XX:+UseFastAccessorMethods
-XX:+HeapDumpOnOutOfMemoryError -Dcom.sun.management.jmxremote.port=7009
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false -verbose:gc -XX:+PrintGCDetails
-XX:+PrintGCTimeStamps
-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
-Djava.util.logging.config.file=/opt/apache-tomcat-6.0.18/conf/logging.properties
-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n
-Djava.endorsed.dirs=/opt/apache-tomcat-6.0.18/endorsed
-classpath :/opt/apache-tomcat-6.0.18/bin/bootstrap.jar
java version "1.6.0_12"
Java(TM) SE Runtime Environment (build 1.6.0_12-b04)
Java HotSpot(TM) 64-Bit Server VM (build 11.2-b01, mixed mode)
After some time of work we get (via JConsole) the following memory consumption:
Current heap size: 3 034 233 kbytes
Maximum heap size: 6 504 832 kbytes
Committed memory: 6 504 832 kbytes
Pending finalization: 0 objects
Garbage collector: Name = 'PS MarkSweep', Collections = 128, Total time spent = 16 minutes
Garbage collector: Name = 'PS Scavenge', Collections = 1 791, Total time spent = 17 minutes
Operating System: Linux 2.6.26-2-amd64
Architecture: amd64
Number of processors: 2
Committed virtual memory: 9 148 856 kbytes
Total physical memory: 8 199 684 kbytes
Free physical memory: 48 060 kbytes
Total swap space: 19 800 072 kbytes
Free swap space: 15 910 212 kbytes
The question is why do we have a lot of committed virtual memory? Note that max heap size is ~7Gb (as expected since Xmx=7G).
top shows the following:
31413 root 18 -2 8970m 7.1g 39m S 90 90.3 351:17.87 java
Why does JVM need additional 2Gb! of virtual memory? Can I get non-heap memory disrtibution just like in JRockit http://blogs.oracle.com/jrockit/2009/02/why_is_my_jvm_process_larger_t.html ?
Edit 1: Perm is 36M.