--- a/src/share/vm/gc/g1/g1CollectedHeap.cpp	Thu Sep 03 08:57:16 2015 -0700
+++ b/src/share/vm/gc/g1/g1CollectedHeap.cpp	Fri Sep 04 08:36:13 2015 +0200
@@ -2923,9 +2923,9 @@
 }
 
 // For G1 TLABs should not contain humongous objects, so the maximum TLAB size
-// must be smaller than the humongous object limit.
+// must be equal to the humongous object limit.
 size_t G1CollectedHeap::max_tlab_size() const {
-  return align_size_down(_humongous_object_threshold_in_words - 1, MinObjAlignment);
+  return align_size_down(_humongous_object_threshold_in_words, MinObjAlignment);
 }
 
 size_t G1CollectedHeap::unsafe_max_tlab_alloc(Thread* ignored) const {

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/gc/g1/TestPLABSizeBounds.java	Fri Sep 04 08:36:13 2015 +0200
@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2015, 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 TestPLABSizeBounds
+ * @bug 8134857
+ * @summary Regression test to ensure that G1 supports PLAB sizes of half a region size.
+ * @requires vm.gc=="G1" | vm.gc=="null"
+ * @key gc
+ * @library /testlibrary
+ * @modules java.base/sun.misc
+ *          java.management
+ */
+
+import java.util.ArrayList;
+
+import jdk.test.lib.OutputAnalyzer;
+import jdk.test.lib.Platform;
+import jdk.test.lib.ProcessTools;
+
+public class TestPLABSizeBounds {
+
+    public static final int M = 1024 * 1024;
+
+    /**
+     * Starts the VM with the given region size and the given PLAB size arguments. The VM start should
+     * succeed if shouldSucceed is true, otherwise it should fail.
+     *
+     * @param regionSize The region size the VM should be started with in bytes.
+     * @param plabSize The young and old gen PLAB sizes the VM should be started with in machine words.
+     * @param shouldSucceed The expected result of the VM invocation.
+     */
+    public static void runTest(int regionSize, int plabSize, boolean shouldSucceed) throws Exception {
+        ArrayList<String> testArguments = new ArrayList<String>();
+
+        testArguments.add("-XX:+UseG1GC");
+        testArguments.add("-Xmx256M");
+        testArguments.add("-XX:G1HeapRegionSize=" + regionSize);
+        testArguments.add("-XX:YoungPLABSize=" + plabSize);
+        testArguments.add("-XX:OldPLABSize=" + plabSize);
+        testArguments.add(GCTest.class.getName());
+
+        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(testArguments.toArray(new String[0]));
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+        if (shouldSucceed) {
+            output.shouldHaveExitValue(0);
+        } else {
+            output.shouldHaveExitValue(1);
+        }
+    }
+
+    public static void runRegionTest(int regionSize) throws Exception {
+        final int regionSizeInBytes = regionSize * M;
+        final int wordSize = Platform.is32bit() ? 4 : 8;
+
+        runTest(regionSizeInBytes, (regionSizeInBytes / wordSize) / 2 - 1, true);
+        runTest(regionSizeInBytes, (regionSizeInBytes / wordSize) / 2, true);
+        runTest(regionSizeInBytes, (regionSizeInBytes / wordSize) / 2 + 1, false);
+    }
+
+    public static void main(String[] args) throws Exception {
+        runRegionTest(1);
+        runRegionTest(2);
+        runRegionTest(4);
+        runRegionTest(8);
+        runRegionTest(16);
+        runRegionTest(32);
+    }
+
+    static class GCTest {
+        public static void main(String [] args) {
+            System.out.println("Test completed.");
+        }
+    }
+}
+