How to make JVM exhaust memory back to OS

Question

I am using the GC XX:+UseParNewGC-XX:+UseConcMarkSweepGC for my application.

Since most of you are already testing the JVM, it is useful to grow the heap to the maximum heap size, however it does not free memory back to the OS. I came across -XX:MaxHeapFreeRatio and -XX:MinHeapFreeRatio , but they are ignored for Parallel Garbage Collectors.

Are there any special options for forcibly unloading JVM memory back to the OS for the combination -XX:MaxHeapFreeRatio and -XX:MinHeapFreeRatio .

Answer 1

On my Java 1.8.0_45 -XX: + UseG1GC reduces memory. This is my test:

  MemoryPoolMXBean m = ManagementFactory.getMemoryPoolMXBeans().get(5); System.out.println(m.getName()); byte[] a = new byte[512 * 1024 * 1024]; System.out.println(m.getUsage().getCommitted() / 1024 / 1024); a = null; System.gc(); Thread.sleep(1000); System.out.println(m.getUsage().getCommitted() / 1024 / 1024);