In Java 8 The concept of Permanent Generation (PermGen) space is removed and it replaced by a new space called Metaspace. The drawback of PermGen removal is that the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error. The PermGen can take Fixed size at startup so it difficult to tune.

Metaspace in Java 8

Metaspace will takes the size at runtime according to the application demand . It dynamically re-size according to the application requirement.

Metaspace memory allocation:- the most of allocation for class metadata are allocated out of native memory and the classes that are used to describe the class metadata is removed. it uses flag named as MaxMetaspaceSize, allowing you to limit the amount of native memory used for class metadata. In case if you dont specify the flag, the Metaspace will takes the size at runtime depending of the application demand at runtime.

Metaspace garbage collection:- Garbage collection of the unused classes or the dead classes and classloaders is triggered only once when the class metadata usage reaches the MaxMetaspaceSize.

Java heap space impact:- some of the data has been moved to the Java heap space. This means there is possibility that you will observe an increase of the Java heap space following a future JDK 8 upgrade.