8013791: G1: G1CollectorPolicy::initialize_flags() may set min_alignment > max_alignment

Summary: Make sure max alignemnt is at least as large as min alignment
Reviewed-by: johnc, jmasa, tschatzl

src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp

@@ -309,7 +309,8 @@ G1CollectorPolicy::G1CollectorPolicy() :
 
 void G1CollectorPolicy::initialize_flags() {
   set_min_alignment(HeapRegion::GrainBytes);
-  set_max_alignment(GenRemSet::max_alignment_constraint(rem_set_name()));
+  size_t card_table_alignment = GenRemSet::max_alignment_constraint(rem_set_name());
+  set_max_alignment(MAX2(card_table_alignment, min_alignment()));
   if (SurvivorRatio < 1) {
     vm_exit_during_initialization("Invalid survivor ratio specified");
   }

src/share/vm/memory/collectorPolicy.cpp

@@ -48,6 +48,13 @@
 // CollectorPolicy methods.
 
 void CollectorPolicy::initialize_flags() {
+  assert(max_alignment() >= min_alignment(),
+      err_msg("max_alignment: " SIZE_FORMAT " less than min_alignment: " SIZE_FORMAT,
+          max_alignment(), min_alignment()));
+  assert(max_alignment() % min_alignment() == 0,
+      err_msg("max_alignment: " SIZE_FORMAT " not aligned by min_alignment: " SIZE_FORMAT,
+          max_alignment(), min_alignment()));
+
   if (MetaspaceSize > MaxMetaspaceSize) {
     MaxMetaspaceSize = MetaspaceSize;
   }
@@ -201,9 +208,6 @@ void GenCollectorPolicy::initialize_flags() {
   // All sizes must be multiples of the generation granularity.
   set_min_alignment((uintx) Generation::GenGrain);
   set_max_alignment(compute_max_alignment());
-  assert(max_alignment() >= min_alignment() &&
-         max_alignment() % min_alignment() == 0,
-         "invalid alignment constraints");
 
   CollectorPolicy::initialize_flags();
 

test/gc/g1/TestRegionAlignment.java

+/*
+ * 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 TestRegionAlignment.java
+ * @bug 8013791
+ * @summary Make sure that G1 ergonomics pick a heap size that is aligned with the region size
+ * @run main/othervm -XX:+UseG1GC -XX:G1HeapRegionSize=32m -XX:MaxRAM=555m TestRegionAlignment
+ *
+ * When G1 ergonomically picks a maximum heap size it must be aligned to the region size.
+ * This test tries to get the VM to pick a small and unaligned heap size (by using MaxRAM=555) and a
+ * large region size (by using -XX:G1HeapRegionSize=32m). This will fail without the fix for 8013791.
+ */
+public class TestRegionAlignment {
+    public static void main(String[] args) { }
+}