JMH: invalid initial heap size

Question

I test my program performance with JMH. And fail to configure heap size. I wondering why it doesn't work.

Questions:

1. Why JMH doesn't accept heap size configs?
2. Does JMH absorb idea heap size settings without jvmArgs method?

Error:

# Run progress: 0.00% complete, ETA 00:04:30
# VM invoker: /usr/lib/jvm/java-8-oracle/jre/bin/java
# VM options: -Xms2048m -Xmx2048m -XX:MaxDirectMemorySize=512M
# Fork: 1 of 1
Invalid initial heap size: -Xms2048m -Xmx2048m -XX:MaxDirectMemorySize=512M
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
<forked VM failed with exit code 1>

Main Method:

public static void main(String... args) throws RunnerException, IOException {
    Options opt = new OptionsBuilder()
            .include(".*" + ArraySummatorBenchmarking.class.getSimpleName() + ".*")
            .warmupIterations(5)
            .measurementIterations(5)
            .forks(1)
            .jvmArgs("-Xms2048m -Xmx2048m -XX:MaxDirectMemorySize=512M")
            .build();
    new Runner(opt).run();
}

idea.vmoptions

-server
-Xms2056m
-Xmx2056m
-XX:MaxPermSize=1024m
-XX:ReservedCodeCacheSize=256m
-ea
-Dsun.io.useCanonCaches=false
-Djava.net.preferIPv4Stack=true
-Djsse.enableSNIExtension=false
-XX:+UseCodeCacheFlushing
-XX:+UseConcMarkSweepGC
-XX:SoftRefLRUPolicyMSPerMB=50
-Dawt.useSystemAAFontSettings=lcd

Main method options:

-Xms2048m -Xmx2048m -XX:MaxDirectMemorySize=512M

Solution

JMH uses Runtime.exec(String[]) to launch a forked VM. This method assumes a single command-line token per array item, and it will properly escape spaces inside tokens.

It means that when you pass a "-Xms2048m -Xmx2048m -XX:MaxDirectMemorySize=512M" string as an argument it is treated as a single argument that happens to contain spaces inside instead of three separate space-separated arguments.

Thus the proper way to specify multiple JVM arguments in JMH is to use a separate string value for each separate argument:

Options opt = new OptionsBuilder()
        ...
        .jvmArgs("-Xms2048m", "-Xmx2048m", "-XX:MaxDirectMemorySize=512M")
        ...