test/jdk/java/lang/management/MemoryMXBean/LowMemoryTest.java

@@ -81,13 +81,17 @@
         final String g1Flag = "-XX:G1HeapRegionSize=1m";
 
         // Runs the test collecting subprocess I/O while it's running.
         traceTest(classMain + ", -XX:+UseSerialGC", nmFlag, lpFlag, "-XX:+UseSerialGC");
         traceTest(classMain + ", -XX:+UseParallelGC", nmFlag, lpFlag, "-XX:+UseParallelGC");
-        traceTest(classMain + ", -XX:+UseG1GC", nmFlag, lpFlag, "-XX:+UseG1GC", g1Flag);
+        traceTest(classMain + ", -XX:+UseG1GC -XX:-G1UseLegacyMonitoring", nmFlag, lpFlag,
+                  "-XX:+UseG1GC", "-XX:-G1UseLegacyMonitoring", g1Flag);
+        traceTest(classMain + ", -XX:+UseG1GC -XX:+G1UseLegacyMonitoring", nmFlag, lpFlag,
+                  "-XX:+UseG1GC", "-XX:+G1UseLegacyMonitoring", g1Flag);
         if (!Compiler.isGraalEnabled()) { // Graal does not support CMS
-            traceTest(classMain + ", -XX:+UseConcMarkSweepGC", nmFlag, lpFlag, "-XX:+UseConcMarkSweepGC");
+             traceTest(classMain + ", -XX:+UseConcMarkSweepGC", nmFlag, lpFlag,
+                       "-XX:+UseConcMarkSweepGC");
         }
     }
 
     /*
      * Creating command-line for running subprocess JVM:

@@ -230,21 +234,43 @@
 
             // Find the Old generation which supports low memory detection
             ListIterator iter = pools.listIterator();
             while (iter.hasNext()) {
                 MemoryPoolMXBean p = (MemoryPoolMXBean) iter.next();
+                // Only check heap pools that support a usage threshold.
+                // This is typically only the old generation space
+                // since the other spaces are expected to get filled up.
                 if (p.getType() == MemoryType.HEAP &&
                     p.isUsageThresholdSupported()) {
+                    // In all collectors except G1, only the old generation supports a
+                    // usage threshold. The G1 legacy mode "G1 Old Gen" also does. In
+                    // G1 default mode, both the old space ("G1 Old Space": it's not
+                    // really a generation in the non-G1 collector sense) and the
+                    // humongous space ("G1 Humongous Space"), support a usage threshold.
+                    // So, the following condition is true for all non-G1 old generations,
+                    // for the G1 legacy old gen, and for the G1 default humongous space.
+                    // It is not true for the G1 default old gen.
+                    //
+                    // We're allocating humongous objects in this test, so the G1 default
+                    // mode "G1 Old Space" occupancy doesn't change, because humongous
+                    // objects are allocated in the "G1 Humongous Space". If we allowed
+                    // the G1 default mode "G1 Old Space", notification would never
+                    // happen because no objects are allocated there.
+                    if (!p.getName().equals("G1 Old Space")) {
                     mpool = p;
                     if (trace) {
                         System.out.println("Selected memory pool for low memory " +
                             "detection.");
                         MemoryUtil.printMemoryPool(mpool);
                     }
                     break;
                 }
             }
+            }
+            if (mpool == null) {
+                throw new RuntimeException("TEST FAILED: No heap pool found");
+            }
 
             TestListener listener = new TestListener();
             SensorListener l2 = new SensorListener();
             NotificationEmitter emitter = (NotificationEmitter) mm;
             emitter.addNotificationListener(listener, null, null);