Scale DNSS expected ratio min/max 2x for InstantOn

This patch scales dnssExpectedRatioMaximum and dnssExpectedRatioMinimum by 2x when neither is user-specified and either CRIU or CRaC support is enabled. This favours reduced memory consumption at the expense of GC overhead. Signed-off-by: Younes Manton <[email protected]>
eclipse-openj9 · Nov 13, 2024 · 0aab9d6 · 0aab9d6
1 parent 32d32bc
commit 0aab9d6
Showing 1 changed file with 16 additions and 0 deletions.
diff --git a/runtime/gc_glue_java/ConfigurationDelegate.hpp b/runtime/gc_glue_java/ConfigurationDelegate.hpp
@@ -117,6 +117,22 @@ class MM_ConfigurationDelegate
 		if (!_extensions->dynamicClassUnloadingKickoffThresholdForced) {
 			_extensions->dynamicClassUnloadingKickoffThreshold = DYNAMIC_CLASS_UNLOADING_KICKOFF_THRESHOLD;
 		}
+
+#if defined(J9VM_OPT_CRIU_SUPPORT)
+		/* Favour reduced memory consumption over pause times when checkpointing is enabled by
+		 * scaling the default min and max DNSS expected ratios by a constant factor, unless
+		 * at least one ratio was directly specified by the user.
+		 */
+		if (javaVM->internalVMFunctions->isCRaCorCRIUSupportEnabled(javaVM)) {
+			const double scaleFactor = 2;
+			if (!_extensions->dnssExpectedRatioMaximum._wasSpecified &&
+			    !_extensions->dnssExpectedRatioMinimum._wasSpecified) {
+				_extensions->dnssExpectedRatioMaximum._valueSpecified *= scaleFactor;
+				_extensions->dnssExpectedRatioMinimum._valueSpecified *= scaleFactor;
+			}
+		}
+#endif /* defined(J9VM_OPT_CRIU_SUPPORT) */
+
 		return true;
 	}