[jboss-user] [Installation, Configuration & DEPLOYMENT] - Re: top command show wrong memory for java

PeterJ do-not-reply at jboss.com
Tue Oct 14 11:02:42 EDT 2008

Let's see:

6144MB for the heap
+256MB for the permgen
+256KB * number of threads for the stacks (the 256KB is a guess, I cannot offhand recall how big each thread stack is)
+xxxMB C/C++ data overhead (this is the JVM's data used to manage/run the Java app)
+xxxMB for the code (the JVM and the shared objects it uses)
7775MB total

Moral of the story - the heap is not everything, there is a lot of overhead above and beyond the heap.

By the way, do you really want a 6BG heap? I hope you are using the CMS collector or else you will wait a long time for each major garbage collection.

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