Modified understanding how to override JVM max heap size section

Author: subhtk

modules/nodes-cluster-resource-configure-jdk.adoc

@@ -29,29 +29,25 @@ this documentation, and may involve setting multiple additional JVM options.
 == Understanding how to override the JVM maximum heap size
 
 For many Java workloads, the JVM heap is the largest single consumer of memory.
-Currently, the OpenJDK defaults to allowing up to 1/4 (1/`-XX:MaxRAMFraction`)
-of the compute node's memory to be used for the heap, regardless of whether the
-OpenJDK is running in a container or not. It is therefore *essential* to
-override this behavior, especially if a container memory limit is also set.
-
-There are at least two ways the above can be achieved:
 
-* If the container memory limit is set and the experimental options are
-   supported by the JVM, set `-XX:+UnlockExperimentalVMOptions
-   -XX:+UseCGroupMemoryLimitForHeap`.
+Currently, on bare metal or VM setups, the OpenJDK's default heap value is 25%, 1/4th of the compute node’s memory. However, within containers using cgroups detection (v1 and v2 for JDK 11/17), Xmx was set as 50% of the max memory resource limits by default. In ubi9 - RHEL 9 images, the default allocation is 80%(set via -XX:MaxRAMPercentage), leaving 20% for native use. It is therefore *essential* to
+override this behavior, especially if a container memory limit is also set.
 +
-[NOTE]
+[IMPORTANT]
 ====
-The `UseCGroupMemoryLimitForHeap` option has been removed in JDK 11. Use `-XX:+UseContainerSupport` instead.
+The `UseContainerSupport` flag is enabled by default in the JVM. It helps the JVM recognize Docker container operations by fetching the container details like CPU count and total memory. Therefore, it is not necessary to manually define `JAVA_MAX_INITIAL_MEM`, as the JVM obtains maximum memory allocation from the pods directly.
 ====
-+
-This sets `-XX:MaxRAM` to the container memory limit, and the maximum heap size
-(`-XX:MaxHeapSize` / `-Xmx`) to 1/`-XX:MaxRAMFraction` (1/4 by default).
 
-* Directly override one of `-XX:MaxRAM`, `-XX:MaxHeapSize` or `-Xmx`.
+To achieve this, directly override one of `-XX:MaxRAM`, `-XX:MaxHeapSize` or `MaxRAMPercentage`.
++
+Because you must provide a specific value, this option helps to calculate a safety margin.
 +
-This option involves hard-coding a value, but has the advantage of allowing a
-safety margin to be calculated.
+[IMPORTANT]
+====
+Prior to JDK17, note that `MaxRAMPercentage` used `MaxRAM`, instead of system memory. The default maximum value for `MaxRAM` is set to `128g`. For example, a container with a `200g` memory limit, using `-XX:MaxRAMPercentage=50` results in a `64g` maximum heap instead of `100g`.
+
+To address this issue in environments with more than `128g` of available memory, a workaround is to explicitly set `MaxRAM` to a higher value. For instance, using `-XX:MaxRAMPercentage=50` `-XX:MaxRAM=200g` would result in a `100g` maximum heap within a container with a `200g` memory limit.
+====
 
 [id="nodes-cluster-resource-configure-jdk-unused_{context}"]
 == Understanding how to encourage the JVM to release unused memory to the operating system