Java memory off heap inside container

Question

I have been studying and reading some questions about memory usage, even with good answers here I would like to try understading some values that I have collected in my analysis.

I wrote this below code just to show where I collected the data. Note: This codes does not compile, it is just to understand.

       long KB_FACTOR = 1024;
        long MB_FACTOR = 1024 * KB_FACTOR;

        OperatingSystemMXBean os = (com.sun.management.OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
        "operationSystem.totalPhysicalMemorySizeMB" = os.getTotalPhysicalMemorySize() / MB_FACTOR);
        "operationSystem.freePhysicalMemorySizeMB"  = os.getFreePhysicalMemorySize() / MB_FACTOR);

        long freeMemoryBytes = Runtime.getRuntime().freeMemory();
        long totalMemoryBytes = Runtime.getRuntime().totalMemory();
        long maxMemoryBytes = Runtime.getRuntime().maxMemory();
        "memory.maxMB" = (maxMemoryBytes / MB_FACTOR);
        "memory.freeMB" = (freeMemoryBytes / MB_FACTOR);
        "memory.totalMB" = (totalMemoryBytes / MB_FACTOR);

        MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();
        MemoryUsage heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        "memoryHeap.commitedMB" = (heapMemoryUsage.getCommitted() / MB_FACTOR);
        "memoryHeap.maxMB" = (heapMemoryUsage.getMax() / MB_FACTOR);

        MemoryUsage nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
       "memoryNonHeap.commitedMB" =  (nonHeapMemoryUsage.getCommitted() / MB_FACTOR);
       "memoryNonHeap.maxMB" = (nonHeapMemoryUsage.getMax() / MB_FACTOR);

       "memoryHeap+NonHeap.committedMB" = (heapMemoryUsage.getCommitted() / MB_FACTOR) + (nonHeapMemoryUsage.getCommitted() / MB_FACTOR);

This is some data I have collected: Container 01

 {
        "memory": {
            "freeMB": 611,
            "maxMB": 1622,
            "totalMB": 1336
        },
        "memoryHeap": {
            "committedMB": 1336,
            "maxMB": 1622
        },
        "memoryNonHeap": {
            "initMB": 7,
            "usedMB": 219,
            "committedMB": 227,
            "maxMB": 0
        },
        "memoryHeap+NonHeap": {
            "committedMB": 1563
        },
        "operationSystem": {
            "totalPhysicalMemorySizeMB": 1907,
            "freePhysicalMemorySizeMB": 390
        }
    }

Container 02:

{
    "memory": {
        "freeMB": 303,
        "maxMB": 1622,
        "totalMB": 1336
    },
    "memoryHeap": {
        "committedMB": 1336,
        "maxMB": 1622
    },
    "memoryNonHeap": {
        "committedMB": 244,
        "maxMB": 0
    },
    "memoryHeap+NonHeap": {
        "committedMB": 1580
    },
    "operationSystem": {
        "totalPhysicalMemorySizeMB": 1907,
        "freePhysicalMemorySizeMB": 87
    }
}

I am running with:

• alpine openjdk-11
• Container memory limit: 2GB
• AWS EKS.
• JVM Env: -Djava.net.preferIPv4Stack=true -XX:InitialRAMPercentage=70.0 -XX:MaxRAMPercentage=85.0 -Dfile.encoding=UTF8

I have noticed that "operationSystem.totalPhysicalMemorySizeMB" is the amount of memory JVM understand as available to use.

The parameter "-XX:MaxRAMPercentage=85.0" work as expected. (using 1,907 as reference)

I know that nonHeap memory is off-heap, then should I use nonHeap+heap to calculate the total usage by my application.

Question: My main doubt is about "freePhysicalMemorySizeMB", this value variates a lot between containers even when the committed memories (heap+nonHeap) have the same value .

I read that java can use Native Library (JNI) and this also consume memory.

• Should I reserve more memory beyond the estimate of heap+NonHeap? If yes, is it possible to know how much? Will Garbage Collector clear these others used memory?

• Is it the term "NonHeap" the same as "off-heap"?

Note: My pod is just running java application (and alpine itself)