Reuse direct memory to heap factor

Author: jan-elastic

distribution/tools/server-cli/src/main/java/org/elasticsearch/server/cli/JvmErgonomics.java

@@ -28,6 +28,8 @@
  */
 final class JvmErgonomics {
 
+    static final double DIRECT_MEMORY_TO_HEAP_FACTOR = 0.5;
+
     private JvmErgonomics() {
         throw new AssertionError("No instances intended");
     }
@@ -44,7 +46,7 @@ static List<String> choose(final List<String> userDefinedJvmOptions, Settings no
         final long heapSize = JvmOption.extractMaxHeapSize(finalJvmOptions);
         final long maxDirectMemorySize = JvmOption.extractMaxDirectMemorySize(finalJvmOptions);
         if (maxDirectMemorySize == 0) {
-            ergonomicChoices.add("-XX:MaxDirectMemorySize=" + heapSize / 2);
+            ergonomicChoices.add("-XX:MaxDirectMemorySize=" + (long) (DIRECT_MEMORY_TO_HEAP_FACTOR * heapSize));
         }
 
         final boolean tuneG1GCForSmallHeap = tuneG1GCForSmallHeap(heapSize);

distribution/tools/server-cli/src/main/java/org/elasticsearch/server/cli/MachineDependentHeap.java

@@ -102,10 +102,15 @@ protected int getHeapSizeMb(Settings nodeSettings, MachineNodeRole role, long av
              * could result in ML processes crashing with OOM errors or repeated autoscaling up and down.
              */
             case ML_ONLY -> {
-                if (availableMemory <= (GB * 16)) {
-                    yield mb((long) (availableMemory * .4 * 2 / 3), 4);
+                double heapFractionBelow16GB = 0.4 / (1.0 + JvmErgonomics.DIRECT_MEMORY_TO_HEAP_FACTOR);
+                double heapFractionAbove16GB = 0.1 / (1.0 + JvmErgonomics.DIRECT_MEMORY_TO_HEAP_FACTOR);
+                if (availableMemory <= GB * 16) {
+                    yield mb((long) (availableMemory * heapFractionBelow16GB), 4);
                 } else {
-                    yield mb((long) min(((GB * 16) * .4 + (availableMemory - GB * 16) * .1) * 2 / 3, MAX_HEAP_SIZE), 4);
+                    yield mb(
+                        (long) min(GB * 16 * heapFractionBelow16GB + (availableMemory - GB * 16) * heapFractionAbove16GB, MAX_HEAP_SIZE),
+                        4
+                    );
                 }
             }
             /*