--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/gc/g1/TestShrinkDefragmentedHeap.java	Thu Sep 11 14:21:13 2014 +0200
@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test TestShrinkDefragmentedHeap
+ * @bug 8038423
+ * @summary Verify that heap shrinks after GC in the presence of fragmentation due to humongous objects
+ *     1. allocate small objects mixed with humongous ones
+ *        "ssssHssssHssssHssssHssssHssssHssssH"
+ *     2. release all allocated object except the last humongous one
+ *        "..................................H"
+ *     3. invoke gc and check that memory returned to the system (amount of committed memory got down)
+ *
+ * @library /testlibrary
+ */
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryUsage;
+import java.util.ArrayList;
+import java.util.List;
+import sun.management.ManagementFactoryHelper;
+import static com.oracle.java.testlibrary.Asserts.*;
+import com.oracle.java.testlibrary.ProcessTools;
+import com.oracle.java.testlibrary.OutputAnalyzer;
+
+public class TestShrinkDefragmentedHeap {
+    // Since we store all the small objects, they become old and old regions are also allocated at the bottom of the heap
+    // together with humongous regions. So if there are a lot of old regions in the lower part of the heap,
+    // the humongous regions will be allocated in the upper part of the heap anyway.
+    // To avoid this the Eden needs to be big enough to fit all the small objects.
+    private static final int INITIAL_HEAP_SIZE  = 200 * 1024 * 1024;
+    private static final int MINIMAL_YOUNG_SIZE = 190 * 1024 * 1024;
+    private static final int REGION_SIZE        = 1 * 1024 * 1024;
+
+    public static void main(String[] args) throws Exception, Throwable {
+        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+                "-XX:InitialHeapSize=" + INITIAL_HEAP_SIZE,
+                "-Xmn" + MINIMAL_YOUNG_SIZE,
+                "-XX:MinHeapFreeRatio=10",
+                "-XX:MaxHeapFreeRatio=11",
+                "-XX:+UseG1GC",
+                "-XX:G1HeapRegionSize=" + REGION_SIZE,
+                "-verbose:gc",
+                GCTest.class.getName()
+        );
+
+        OutputAnalyzer output = ProcessTools.executeProcess(pb);
+        output.shouldHaveExitValue(0);
+    }
+
+    static class GCTest {
+
+        private static final String MIN_FREE_RATIO_FLAG_NAME = "MinHeapFreeRatio";
+        private static final String MAX_FREE_RATIO_FLAG_NAME = "MaxHeapFreeRatio";
+        private static final String NEW_SIZE_FLAG_NAME = "NewSize";
+
+        private static final ArrayList<ArrayList<byte[]>> garbage = new ArrayList<>();
+
+        private static final int SMALL_OBJS_SIZE  = 10 * 1024; // 10kB
+        private static final int SMALL_OBJS_COUNT = MINIMAL_YOUNG_SIZE / (SMALL_OBJS_SIZE-1);
+        private static final int ALLOCATE_COUNT = 3;
+        // try to put all humongous object into gap between min young size and initial heap size
+        // to avoid implicit GCs
+        private static final int HUMONG_OBJS_SIZE = (int) Math.max(
+                (INITIAL_HEAP_SIZE - MINIMAL_YOUNG_SIZE) / ALLOCATE_COUNT / 4,
+                REGION_SIZE * 1.1
+        );
+
+        private static final long initialHeapSize = getHeapMemoryUsage().getUsed();
+
+        public static void main(String[] args) throws InterruptedException {
+            new GCTest().test();
+        }
+
+        private void test() throws InterruptedException {
+            MemoryUsagePrinter.printMemoryUsage("init");
+
+            allocate();
+            System.gc();
+            MemoryUsage muFull = getHeapMemoryUsage();
+            MemoryUsagePrinter.printMemoryUsage("allocated");
+
+            free();
+            //Thread.sleep(1000); // sleep before measures due lags in JMX
+            MemoryUsage muFree = getHeapMemoryUsage();
+            MemoryUsagePrinter.printMemoryUsage("free");
+
+            assertLessThan(muFree.getCommitted(), muFull.getCommitted(), prepareMessageCommittedIsNotLess() );
+        }
+
+        private void allocate() {
+            System.out.format("Will allocate objects of small size = %s and humongous size = %s",
+                    MemoryUsagePrinter.humanReadableByteCount(SMALL_OBJS_SIZE, false),
+                    MemoryUsagePrinter.humanReadableByteCount(HUMONG_OBJS_SIZE, false)
+            );
+
+            for (int i = 0; i < ALLOCATE_COUNT; i++) {
+                ArrayList<byte[]> stuff = new ArrayList<>();
+                allocateList(stuff, SMALL_OBJS_COUNT / ALLOCATE_COUNT, SMALL_OBJS_SIZE);
+                garbage.add(stuff);
+
+                ArrayList<byte[]> humongousStuff = new ArrayList<>();
+                allocateList(humongousStuff, 4, HUMONG_OBJS_SIZE);
+                garbage.add(humongousStuff);
+            }
+        }
+
+        private void free() {
+            // do not free last one list
+            garbage.subList(0, garbage.size() - 1).clear();
+
+            // do not free last one element from last list
+            ArrayList stuff = garbage.get(garbage.size() - 1);
+            if (stuff.size() > 1) {
+                stuff.subList(0, stuff.size() - 1).clear();
+            }
+            System.gc();
+        }
+
+        private String prepareMessageCommittedIsNotLess() {
+            return String.format(
+                    "committed free heap size is not less than committed full heap size, heap hasn't been shrunk?%n"
+                    + "%s = %s%n%s = %s",
+                    MIN_FREE_RATIO_FLAG_NAME,
+                    ManagementFactoryHelper.getDiagnosticMXBean().getVMOption(MIN_FREE_RATIO_FLAG_NAME).getValue(),
+                    MAX_FREE_RATIO_FLAG_NAME,
+                    ManagementFactoryHelper.getDiagnosticMXBean().getVMOption(MAX_FREE_RATIO_FLAG_NAME).getValue()
+            );
+        }
+
+        private static void allocateList(List garbage, int count, int size) {
+            for (int i = 0; i < count; i++) {
+                garbage.add(new byte[size]);
+            }
+        }
+    }
+
+    static MemoryUsage getHeapMemoryUsage() {
+        return ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();
+    }
+
+    /**
+     * Prints memory usage to standard output
+     */
+    static class MemoryUsagePrinter {
+
+        public static String humanReadableByteCount(long bytes, boolean si) {
+            int unit = si ? 1000 : 1024;
+            if (bytes < unit) {
+                return bytes + " B";
+            }
+            int exp = (int) (Math.log(bytes) / Math.log(unit));
+            String pre = (si ? "kMGTPE" : "KMGTPE").charAt(exp - 1) + (si ? "" : "i");
+            return String.format("%.1f %sB", bytes / Math.pow(unit, exp), pre);
+        }
+
+        public static void printMemoryUsage(String label) {
+            MemoryUsage memusage = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();
+            float freeratio = 1f - (float) memusage.getUsed() / memusage.getCommitted();
+            System.out.format("[%-24s] init: %-7s, used: %-7s, comm: %-7s, freeRatio ~= %.1f%%%n",
+                    label,
+                    humanReadableByteCount(memusage.getInit(), false),
+                    humanReadableByteCount(memusage.getUsed(), false),
+                    humanReadableByteCount(memusage.getCommitted(), false),
+                    freeratio * 100
+            );
+        }
+    }
+}