--- /dev/null	2020-01-22 09:36:18.061667933 +0100
+++ new/test/hotspot/jtreg/gc/testlibrary/g1/MixedGCProvoker.java	2020-01-22 11:37:59.301818978 +0100
@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2020, 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.
+ */
+
+package gc.testlibrary.g1;
+
+import static java.util.stream.IntStream.range;
+import static jdk.test.lib.Asserts.assertTrue;
+import static sun.hotspot.WhiteBox.getWhiteBox;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import gc.testlibrary.Helpers;
+import jdk.test.lib.Asserts;
+
+/**
+ * Utility class to reliably provoke a mixed GC. The class allocates several arrays and
+ * promotes them to the old generation. All GCs are triggered by Whitebox to ensure that they occur.
+ * Must use G1.
+ */
+public class MixedGCProvoker {
+	
+	/**
+	 * Allocate a few objects that are supposed to end up in the old generation as they are held live by the
+	 * given array. Caller must make sure by running this test with e.g. -XX:+AlwaysTenure that the objects
+	 * to actually be tenured.
+	 * Mixes live and dead objects, allocating about two regions worth of objects.
+	 * @param liveOldObjects Array receiving the live objects after this method.
+	 * @param g1HeapRegionSize Size of a G1 heap region.
+	 * @param arraySize Size of the byte arrays to use.
+	 */
+    public static void allocateOldObjects(
+            List<byte[]> liveOldObjects,
+            int g1HeapRegionSize,
+            int arraySize) {
+
+        var toUnreachable = new ArrayList<byte[]>();
+
+        // Allocates buffer and promotes it to the old gen. Mix live and dead old objects.
+        // allocate about two regions of old memory. At least one full old region will guarantee
+        // mixed collection in the future
+        range(0, g1HeapRegionSize/arraySize).forEach(n -> {
+            liveOldObjects.add(new byte[arraySize]);
+            toUnreachable.add(new byte[arraySize]);
+        });
+
+        // Do one young collection, AlwaysTenure will force promotion.
+        getWhiteBox().youngGC();
+
+        // Check it is promoted & keep alive
+        Asserts.assertTrue(getWhiteBox().isObjectInOldGen(liveOldObjects), "List of the objects is suppose to be in OldGen");
+        Asserts.assertTrue(getWhiteBox().isObjectInOldGen(toUnreachable), "List of the objects is suppose to be in OldGen");
+    }
+
+    /**
+     * Provoke at least one mixed gc by starting a marking cycle, waiting for its end and triggering two GCs.
+     * @param liveOldObjects The objects supposed to survive this marking cycle.
+     */
+    public static void provokeMixedGC(List<byte[]> liveOldObjects) {
+        Helpers.waitTillCMCFinished(getWhiteBox(), 10);
+        getWhiteBox().g1StartConcMarkCycle();
+        Helpers.waitTillCMCFinished(getWhiteBox(), 10);
+        getWhiteBox().youngGC(); // the "Prepare Mixed" gc
+        getWhiteBox().youngGC(); // the "Mixed" gc
+
+        // check that liveOldObjects still alive
+        assertTrue(getWhiteBox().isObjectInOldGen(liveOldObjects), "List of the objects is suppose to be in OldGen");    	
+    }
+
+    /**
+     * Provoke a mixed GC on a G1 heap with the given heap region size.
+     * @param g1HeapRegionSize The size of your regions in bytes
+     */
+    public static void allocateAndProvokeMixedGC(int g1HeapRegionSize) {
+        final var arraySize = 20_000;
+        var liveOldObjects = new ArrayList<byte[]>();
+
+        getWhiteBox().fullGC(); // Make sure the heap is in a known state.
+        allocateOldObjects(liveOldObjects, g1HeapRegionSize, arraySize);
+        provokeMixedGC(liveOldObjects);
+    }
+}