Relation between memory host and memory arguments xms and xmx from Java

Question

I have the following host with the memory details:

$free -m
             total       used       free     shared    buffers     cached
Mem:          7872              


        

Answer 1

Memory used by Java process (as seen by the OS) is not only limited to Java Heap. There are a lot more memory areas that should be also counted:

• Metaspace (where class metadata resides);
• Code Cache (storage for JIT-compiled methods and all the generated code);
• Direct ByteBuffers;
• Memory-mapped files, including files mapped by JVM, e.g. all JAR files on the classpath;
• Thread stacks;
• JVM code itself and all the dynamic libraries loaded by Java Runtime;
• Other internal JVM structures.

Use NativeMemoryTracking JDK feature to get the detailed breakdown of memory areas used by JVM:

java -XX:NativeMemoryTracking=detail -XX:+UnlockDiagnosticVMOptions -XX:+PrintNMTStatistics