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POJava memory as reported with JMX vs. htop
 

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  1. POJava memory as reported with JMX vs. htop
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    <p>I'm trying to debug why a program which prints <code>Hello</code> and then <code>Thread.sleep(3600*1000)</code> uses ~404MB of virtual memory under linux (with both OpenJDK and Sun JVMs) on both CentOS 5 and Ubuntu 10.04 server. (a MediaTemple (dv) and (ve), respectively).</p> <p>But more specifically, when I connect using VisualVM or JConsole I see what looks like reasonable memory usage: 820KM heap (after GC); 8.4MB PermGen; 1136 classes loaded.</p> <p>Why the discrepancy? </p> <p>Is purely having a JVM running using that much memory? I tried starting two Hello apps to see if the memory usage scales linearly, and it does:</p> <p>I started with 78MB of total RAM used. Starting one hello app bumps the memory usage to 376MB. Starting another hello app gives a total RAM usage of 656MB, so memory doesn't seem to be shared well. (these numbers are not virtual memory </p> <p>(these specific numbers are with OpenJDK, but using the Sun 6 JDK gives comprable, but slightly lower memory usage)</p> <p>Code:</p> <pre><code>public class Hello { public static void main(String[] args) throws Throwable { System.out.println("HI"); Thread.sleep(3600 * 1000); return; } } </code></pre> <p>Command Line:</p> <pre><code>java -Xmx32m -Xms32m Hello </code></pre> <p>With JMX:</p> <pre><code> java -Dcom.sun.management.jmxremote.port=8005 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Xmx32m -Xms32m Hello </code></pre> <p>Thank you for your help,</p> <p>Wiktor</p>
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    1. COTo clarify: RES memory for Hello is 21MB (as expected) and SHR memory is 8MB. Both reasonable (well, for Java ;-)). My problem is that the virtual memory usage is subtracted from my total allowance of 2GB, and I need to run ~18 java applications.
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    2. COI tried using `ulimit -v` to adjust virtual memory usage, but unless it's set to about 400,000 (400MB) the java app does not start successfully.
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    3. COI tried using -Djava.awt.headless=true (with both Sun and OpenJDK) without significant effect.
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