Java: Memory usage issue

Question

I've set maxmimum memory this value

java -Xmx280m -jar ...

Code for memory usage information (on button click):

    int mb = 1024*1024;
    //Getting the runtime reference from system
    Runtime runtime = Runtime.getRuntime();
    System.out.println("##### Heap utilization statistics [MB] #####");
    //Print used memory
    System.out.println("Used Memory:"
        + (runtime.totalMemory() - runtime.freeMemory()) / mb);
    //Print free memory
    System.out.println("Free Memory:"
        + runtime.freeMemory() / mb);
    //Print total available memory
    System.out.println("Total Memory:" + runtime.totalMemory() / mb);
    //Print Maximum available memory
    System.out.println("Max Memory:" + runtime.maxMemory() / mb);

The program shows the following output (2 clicks+new tabs etc):

Used Memory:41
Free Memory:123
Total Memory:165
Max Memory:249
Used Memory:67
Free Memory:97
Total Memory:165
Max Memory:249

However, when I look at the Linux (Centos 7) System Monitor it shows 330mbfor this java process. How to explain it?

Maxim Kirilov · Accepted Answer · 2015-06-08 12:46:45Z

2

The JVM memory consists of the following segments:

Heap Memory, which is the storage for Java objects
Non-Heap Memory, which is used by Java to store loaded classes and other meta-data
JVM code itself, JVM internal structures, loaded profiler agent code and data, etc.

Those parts can be configured with flags that passed during process startup:

The memory structure of JVM process

edited Jun 8, 2015 at 12:46

answered Jun 8, 2015 at 12:39

Maxim Kirilov

2,75928 silver badges49 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Maxim Kirilov Over a year ago

This is a vast area, those regions are used for memory management that is done by the JVM. For further information read about garbage collection algorothms.

Kayaman · Accepted Answer · 2015-06-08 12:43:45Z

2

The 280 megabytes you specified is reserved for the Java program's heap. The VM and other things also use memory, so it'll never be the same number on the command line and in the process listing.

answered Jun 8, 2015 at 12:43

Kayaman

73.8k6 gold badges91 silver badges128 bronze badges

Collectives™ on Stack Overflow

Java: Memory usage issue

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related