CODEWITHSUNDEEP
javamemoryjvmvirtual
teddy teddy
teddy teddy

Reputation: 3085

Java Virtual Memory for a no-op program?

For the following no-op code,

public class a {
public static void main(String args[]) throws Exception{
Thread.sleep(100000);
}
}

If I run it on a 64-bit jvm, through "top" I can see that it uses 2GB virtual memory. What is taking up that virtual memory? This example may be weird, but we do see some production code that uses a lot of virtual mem so that it exceeds ulimit -v

Thanks Yang

Upvotes: 3

Views: 300

Answers (2)

Peter Lawrey
Peter Lawrey

Reputation: 533492

When you start a Java application it creates its heap (to its maximum size) on start up. The default size for recent Sun/Oracle JVMs is 1/4 of your main memory. This sounds wasteful, except all it does is reserve address space. Given each application has its own address space, this doesn't matter much. (unless you have a 32-bit JVM with limited address space)

Upvotes: 0

Ben S
Ben S

Reputation: 69342

Virtual memory does not mean that it is actually allocated and being used. It simply means it has that much currently addressable for use if need be.

Upvotes: 4

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