CODEWITHSUNDEEP
javajvm
D.R.
D.R.

Reputation: 21194

Minimum Oracle Java VM heap memory setting?

Is there a minimum -Xmx setting for Oracle's JVM? It looks like -Xmx2M does provide the application with more than 2 MB of heap size, as the Java Memory MX bean tells me it allocates like 10 MB...

Is there a minimum under which the JVM silently ignores the Xmx setting?

Upvotes: 0

Views: 294

Answers (2)

Ashwani
Ashwani

Reputation: 3481

For jvm to start minimum 2mb of heapsize is required. You can set heap size to 0 bytes, but jvm will not start. And maximum heap size recommended is 1/4 of total ram.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533442

If I run

public static void main(String[] args) {
    System.out.println("Heap size is " + Runtime.getRuntime().totalMemory() / 100000 / 10.0 + " MB");
}

with -mx8m on Java 7 update 25 64-bit I get

Heap size is 8.0 MB

but if I run with -mx2m I get

Heap size is 3.2 MB

So it does appear you get slightly more heap than you asked for for very small sizes. However, even for a small mobile device I wouldn't be worrying about every last MB because the JVM itself is much larger (can be over 100 MB of shared memory, thread etc)

i.e. if you can't spare a few MB, you won't be able to run the JVM anyway.

Upvotes: 2

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