8266802: Shenandoah: Round up region size to page size unconditionally

Backport-of: e5d3ee394ae940ee0111489e6e072f327ec29c3b

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -151,7 +151,9 @@ jint ShenandoahHeap::initialize() {
   Universe::check_alignment(init_byte_size, reg_size_bytes, "Shenandoah heap");
 
   _num_regions = ShenandoahHeapRegion::region_count();
-  assert(_num_regions == (max_byte_size / reg_size_bytes), "Must match");
+  assert(_num_regions == (max_byte_size / reg_size_bytes),
+         "Regions should cover entire heap exactly: " SIZE_FORMAT " != " SIZE_FORMAT "/" SIZE_FORMAT,
+         _num_regions, max_byte_size, reg_size_bytes);
 
   // Now we know the number of regions, initialize the heuristics.
   initialize_heuristics();

src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp

@@ -541,10 +541,10 @@ void ShenandoahHeapRegion::setup_sizes(size_t max_heap_size) {
   }
 
   // Make sure region size is at least one large page, if enabled.
-  // Otherwise, uncommitting one region may falsely uncommit the adjacent
-  // regions too.
-  // Also see shenandoahArguments.cpp, where it handles UseLargePages.
-  if (UseLargePages && ShenandoahUncommit) {
+  // The heap sizes would be rounded by heap initialization code by
+  // page size, so we need to round up the region size too, to cover
+  // the heap exactly.
+  if (UseLargePages) {
     region_size = MAX2(region_size, os::large_page_size());
   }
 

test/hotspot/jtreg/gc/shenandoah/options/TestLargePages.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2021, Red Hat, Inc. 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 id=default
+ * @requires vm.gc.Shenandoah
+ *
+ * @run main/othervm -XX:+UseShenandoahGC -Xms128m -Xmx128m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC          -Xmx128m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -Xms128m          TestLargePages
+ *
+ * @run main/othervm -XX:+UseShenandoahGC -Xms131m -Xmx131m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC          -Xmx131m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -Xms131m          TestLargePages
+ */
+
+/*
+ * @test id=lp
+ * @requires vm.gc.Shenandoah
+ *
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseLargePages -Xms128m -Xmx128m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseLargePages          -Xmx128m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseLargePages -Xms128m          TestLargePages
+ *
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseLargePages -Xms131m -Xmx131m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseLargePages          -Xmx131m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseLargePages -Xms131m          TestLargePages
+ */
+
+/*
+ * @test id=thp
+ * @requires vm.gc.Shenandoah
+ * @requires os.family == "linux"
+ *
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseTransparentHugePages -Xms128m -Xmx128m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseTransparentHugePages          -Xmx128m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseTransparentHugePages -Xms128m          TestLargePages
+ *
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseTransparentHugePages -Xms131m -Xmx131m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseTransparentHugePages          -Xmx131m TestLargePages
+ * @run main/othervm -XX:+UseShenandoahGC -XX:+UseTransparentHugePages -Xms131m          TestLargePages
+ */
+
+public class TestLargePages {
+    public static void main(String[] args) {
+        // Everything is checked on initialization
+    }
+}