A DESCRIPTION OF THE REQUEST :
Hello,

One of my JVM is setting the max heap size (-Xmx1024m) to 1 GB. When the memory was peak, I saw:

Max = 910 MB (This value is from runtime.maxMemory())
Committed = 1002 MB (This value is from runtime.totalMemory())
Used = 978 MB (This value is from runtime.totalMemory() - runtime.freeMemory())

I saw the memory usage percent around 107%. I also confuse why the max heap size is not equal to the one I set (1024 MB).

I'm using Oracle JDK 1.7.0_40.

Regards,
Pornpan

JUSTIFICATION :
When I calculated the memory usage percentage should not over 100%.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
runtime.maxMemory() = the value of -Xmx param
ACTUAL -
$ /usr/java/jdk1.7.0_40/bin/java -Xmx1024m TestMemory
##### Heap utilization statistics [MB] #####
Used Memory:3
Free Memory:659
Total Memory:662
Max Memory:910

---------- BEGIN SOURCE ----------
public class TestMemory {

    public static void main(String [] args) {

        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);
    }
}

---------- END SOURCE ----------