Is there a way to measure direct memory usage in Java?

Question

If I create a buffer via `ByteBuffer.allocateDirect()`, the memory exists outside of the Java heap. Is there a way to measure this kind of memory usage from my application in a cross-platform way similar to how I can measure Java heap usage with `Runtime.totalMemory()` and `Runtime.freeMemory()`?

Accepted Answer

You can use reflections to get `Bits.reservedMemory` on OpenJDK/HotSpot Java 7. There is no platform independent way and this only shows you the usage via ByteBuffer.allocateDirect() not any other way of allocating native memory.

An alternative is to parse `/proc/{pid}/maps` and exclude file mappings. This is an approximation of the virtual memory your process is using.

Is there a way to measure direct memory usage in Java?

Solution

Problem