title: JVM configuration on 64-bit Linux
body: <p>I have a server application that runs on 64-bit Ubuntu server with 4Gb RAM.
  When I set JVM (We use Sun JVM 1.6) configuration parameters like this: -Xms1024m -Xmx2560m, I see a strange memory allocation when starting the application (It runs on Tomcat 6).
  Ubuntu's "top" command shows that the virtual memory size is almost 3,2Gb. I don't understand whether Ubuntu allocated the memory I asked for when starting the JVM, or maybe Ubuntu adds a part swap to the -Xmx value and thus I get this big size. 
  If I run on 32-bit Ubuntu server and configure -Xmx1536m I see 1721m when running "top" command. Can anybody explain me what are those deltas and when they come from?
  I have other processes running on those instances and I want to understand what memory configuration I should apply for them taking into account the results of Ubuntu's "top" command.</p>
  
  <p>Thanks in advance,
  Alex</p>