Perm gen is short for permanent generation. Perm gen is used with version 7 of Java, and metaspace is used with version 8 of Java. Perm gen / metaspace is memory that is allocated for certain tasks, such as keeping a declaration of the classes being used by the Java application.

The following JVM arguments are used to configure the max perm gen / metaspace size for the JVM (256 MB in this example). These options would be set in the JVMs wrapper.conf file, which should be located at mule_home/server_name/conf/wrapper.conf. If you change the minimum or maximum perm gen / metaspace size, you will need to restart the JVM for the change to take effect.

# Initial / Minimum Perm Gen Size
-XX:PermSize=256m

# Maximum Perm Gen Size
-XX:MaxPermSize=256m

# Maximum Metaspace Size
-XX:MaxMetaspaceSize=256m