--- a/hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp	Thu Aug 01 07:03:07 2013 +0200
+++ b/hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp	Thu Aug 01 09:35:04 2013 +0200
@@ -314,6 +314,11 @@
     region_size = MAX_REGION_SIZE;
   }
 
+  if (region_size != G1HeapRegionSize) {
+    // Update the flag to make sure that PrintFlagsFinal logs the correct value
+    FLAG_SET_ERGO(uintx, G1HeapRegionSize, region_size);
+  }
+
   // And recalculate the log.
   region_size_log = log2_long((jlong) region_size);
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/gc/arguments/TestG1HeapRegionSize.java	Thu Aug 01 09:35:04 2013 +0200
@@ -0,0 +1,64 @@
+/*
+* Copyright (c) 2013, 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 TestG1HeapRegionSize
+ * @key gc
+ * @bug 8021879
+ * @summary Verify that the flag G1HeapRegionSize is updated properly
+ * @run main/othervm -Xmx64m TestG1HeapRegionSize 1048576
+ * @run main/othervm -XX:G1HeapRegionSize=2m -Xmx64m TestG1HeapRegionSize 2097152
+ * @run main/othervm -XX:G1HeapRegionSize=3m -Xmx64m TestG1HeapRegionSize 2097152
+ * @run main/othervm -XX:G1HeapRegionSize=64m -Xmx256m TestG1HeapRegionSize 33554432
+ */
+
+import sun.management.ManagementFactoryHelper;
+import com.sun.management.HotSpotDiagnosticMXBean;
+import com.sun.management.VMOption;
+
+public class TestG1HeapRegionSize {
+
+  public static void main(String[] args) {
+    HotSpotDiagnosticMXBean diagnostic = ManagementFactoryHelper.getDiagnosticMXBean();
+
+    VMOption option = diagnostic.getVMOption("UseG1GC");
+    if (option.getValue().equals("false")) {
+      System.out.println("Skipping this test. It is only a G1 test.");
+      return;
+    }
+
+    String expectedValue = getExpectedValue(args);
+    option = diagnostic.getVMOption("G1HeapRegionSize");
+    if (!expectedValue.equals(option.getValue())) {
+      throw new RuntimeException("Wrong value for G1HeapRegionSize. Expected " + expectedValue + " but got " + option.getValue());
+    }
+  }
+
+  private static String getExpectedValue(String[] args) {
+    if (args.length != 1) {
+      throw new RuntimeException("Wrong number of arguments. Expected 1 but got " + args.length);
+    }
+    return args[0];
+  }
+
+}