Start a new java process using Runtime.Exec() seems to ignore the -Xmx

Question

I am working with a process that requires a minimum of 1.5 GB to run and works better if more is available.
So I am determining how much memory is available at startup and restarting the jre by calling
Runtime.exec("java -Dcom.sun.management.jmxremote=true -Xmx1500M -jar XXX.jar")
which reinvokes the same process with a new max memory size.
The initial call to the process is
java -Dcom.sun.management.jmxremote=true -Xmx3500M -jar XXX.jar
The initial call returns 3262251008 from Runtime.maxmemory()
When reinvoked through Runtime.exec() as above
Runtime.maxmemory() still returns 3262251008
Is there a way to separate the new process from the size specified by the parent process?

Answer 1

That is strange. Here is a program I wrote which calls itself recursively.
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.ArrayList;
import static java.util.Arrays.asList;
public class MemorySize {
    public static void main(String... args) throws IOException, InterruptedException {
        System.out.println("Maximum memory size= "+Runtime.getRuntime().maxMemory());
        if (args.length == 0) return;
        List<String> cmd = new ArrayList<String>();
        cmd.add("java");
        cmd.add("-cp");
        cmd.add(System.getProperty("java.class.path"));
        cmd.add("-Xmx"+args[0]+'m');
        cmd.add("MemorySize");
        cmd.addAll(asList(args).subList(1,args.length));
        Process p = new ProcessBuilder(cmd).start();
        readin(p.getErrorStream());
        readin(p.getInputStream());
    private static void readin(final InputStream in) {
        new Thread(new Runnable() {
            public void run() {
                try {
                    byte[] bytes = new byte[1024];
                    int len;
                    while((len = in.read(bytes))>0)
                        System.out.write(bytes, 0, len);
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
        }).start();
}If you run this with the args 128 96 33 222 it prints out
Maximum memory size= 66650112
Maximum memory size= 133234688
Maximum memory size= 99942400
Maximum memory size= 35389440
Maximum memory size= 231014400