Footprint Comparison - OpenJ9 vs. HotSpot

JVM Tutorials - Herong's Tutorial Examples

∟Footprint Comparison - OpenJ9 vs. HotSpot

This section provides a tutorial example on how to compare footprint of OpenJ9 and HotSpot JVMs. My tests show that OpenJ9 footprint is 28% smaller than HotSpot on a CentOS Linux computer.

OpenJ9 document claims that OpenJ9 JVM footprint (measured as RSS, Resident Set Size) is 66% smaller than HotSpot after startup. Here is what I did to verify this on my CentOS computer.

1. Verify OpenJDK/HotSpot installation:

herong$ java -version
openjdk version "11.0.6" 2020-01-14 LTS
OpenJDK Runtime Environment 18.9 (build 11.0.6+10-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.6+10-LTS, mixed mode, sharing)

2. Verify OpenJDK/OpenJ9 installation:

herong$ ./jdk-14.0.1+7-jre/bin/java -version
openjdk version "14.0.1" 2020-04-14
OpenJDK Runtime Environment AdoptOpenJDK (build 14.0.1+7)
Eclipse OpenJ9 VM AdoptOpenJDK (build openj9-0.20.0, JRE 14 Linux ...
OpenJ9   - 05fa2d361
OMR      - d4365f371
JCL      - 5757187cae based on jdk-14.0.1+7)

3. Use a simple Java program, LongWhile.java, to test footprint.

/* LongWhile.java
 * Copyright (c) HerongYang.com, All Rights Reserved.
 */
class LongWhile {
   public static void main(String[] a) {
      Runtime rt = Runtime.getRuntime();
      System.out.println("Total memory: " + rt.totalMemory());
      System.out.println(" Free memory: " + rt.freeMemory());
      System.out.println(" Used memory: "
         + (rt.totalMemory()-rt.freeMemory()));
      while (true);
   }
}

4. Run LongWhile.java with OpenJDK/HotSpot, and measure RSS (Resident Set Size) of the JVM process in two terminal windows:

herong$ java LongWhile.java
Total memory: 127926272
 Free memory: 120359424
 Used memory: 7566848

(on another window)
herong$ ps -ef | grep java
15799 15182 98 02:27 pts/0 ... java LongWhile.java

[herong$ ps -orss --pid 15799
  RSS
88556

[herong$ kill 15799

5. Run LongWhile.java with OpenJDK/OpenJ9, and measure RSS (Resident Set Size) of the JVM process in two terminal windows:

herong$ ./jdk-14.0.1+7-jre/bin/java LongWhile.java
Total memory: 8912896
 Free memory: 2692152
 Used memory: 6220864

(on another window)
[herong$ ps -ef | grep java
15560 15182 99 04:18 pts/0  ... ./jdk-14.0.1+7-jre/bin/java LongWhile.java

[herong$ ps -orss --pid 15560
  RSS
63728

[herong$ kill 15560

6. Compare test results:

               Used     RSS
             Memory    Size
            -------   -----
HotSpot     7566848   88556
OpenJ9      6220864   63728
% Smaller       18%     28%