If you develop Eclipse plug-ins, you are always brought to run an Eclipse application.
It means that to test your plug-ins, you have to launch a second Eclipse from the one where you develop.
One common problem in this case is the PermGen Space issue.
This is in particular true if you test GMF plug-ins or if there is a lot of class generation.
To solve this, you can modify the permgen space allocated when you run the other Eclipse.
Go into Run > Debug Configurations. Select your Eclipse configration and go into the Arguments tab.
The field to upate is the VM Arguments.
As an example, when running Talend Open Studio in debug, I have to use the following settings.
-Xms256m -Xmx1024m -XX:MaxPermSize=512m