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I just installed Eclipse 4.2 (Juno) on Linux 64 bit. I have looked at several Eclipse.ini threads on Stack Overflow, but I still don't understand the relationship between the different memory parameters.
On one hand, there are parameters that are for the VM and that go under -vmargs (for example, -Xms and -Xmx, -XX), while others (for example, --launcher.XXMaxPermSize) are provided to Eclipse directly.
What is the relationship between these parameters? How would I set them up for a machine with more than 8 GB of memory?
I am aware of the long Stack Overflow question What are the best JVM settings for Eclipse?, but I would like to learn how to adjust these parameters myself.
For reference, after installation, the default parameters that Juno has are:
-startup plugins/org.eclipse.equinox.launcher_1.3.0.v20120522-1813.jar --launcher.library plugins/org.eclipse.equinox.launcher.gtk.linux.x86_1.1.200.v20120522-1813 -product org.eclipse.epp.package.cpp.product --launcher.defaultAction openFile -showsplash org.eclipse.platform --launcher.XXMaxPermSize 256m --launcher.defaultAction openFile -vmargs -Dosgi.requiredJavaVersion=1.5 -Dhelp.lucene.tokenizer=standard -XX:MaxPermSize=256m -Xms40m -Xmx512m 
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On the Eclipse menu, clicks Run -> Run Configurations.. , select the Java application we want to run, click on the Arguments tab, VM arguments section, and adjust a better Java initial maximum heap size.
Goto Window > Preferences > General and enable Show heap status and click OK. In the status bar of eclipse (bottom of the screen) a new UI element will appear. We can see 3 things: The amount of used memory by the application (including garbage that has not been collected), in the example 111MB.
The flag Xmx specifies the maximum memory allocation pool for a Java virtual machine (JVM), while Xms specifies the initial memory allocation pool. The Xms flag has no default value, and Xmx typically has a default value of 256 MB.
If you are running Eclipse on an Oracle/Sun JVM, I would disregard --launcher.XXMaxPermSize (I personally remove it) and concentrate on -XX:MaxPermSize, -Xms and -Xmx.
The reason for --launcher.XXMaxPermSize is that some non-Oracle/Sun JVMs would choke on -XX:MaxPermSize. The launcher is programmed to detect the JVM and conditionally supply -XX:MaxPermSize. This of course is defeated by the explicit -XX:MaxPermSize setting in the default eclipse.ini file. That looks like a bug.
I never mess with -Xms setting. I set -Xmx1024m and -XX:MaxPermSize=512m.
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