8053995: Add method to WhiteBox to get vm pagesize.

Summary: Unsafe is not recommended and may deprecated in future. Added a WhiteBox API to get VM page size.
Reviewed-by: dholmes, ccheung, mseledtsov
Contributed-by: yumin.qi@oracle.com

src/share/vm/prims/whitebox.cpp

@@ -73,6 +73,9 @@ WB_ENTRY(jint, WB_GetHeapOopSize(JNIEnv* env, jobject o))
   return heapOopSize;
 WB_END
 
+WB_ENTRY(jint, WB_GetVMPageSize(JNIEnv* env, jobject o))
+  return os::vm_page_size();
+WB_END
 
 class WBIsKlassAliveClosure : public KlassClosure {
     Symbol* _name;
@@ -972,6 +975,7 @@ static JNINativeMethod methods[] = {
   {CC"getObjectSize",      CC"(Ljava/lang/Object;)J", (void*)&WB_GetObjectSize     },
   {CC"isObjectInOldGen",   CC"(Ljava/lang/Object;)Z", (void*)&WB_isObjectInOldGen  },
   {CC"getHeapOopSize",     CC"()I",                   (void*)&WB_GetHeapOopSize    },
+  {CC"getVMPageSize",      CC"()I",                   (void*)&WB_GetVMPageSize     },
   {CC"isClassAlive0",      CC"(Ljava/lang/String;)Z", (void*)&WB_IsClassAlive      },
   {CC"classKnownToNotExist",
                            CC"(Ljava/lang/ClassLoader;Ljava/lang/String;)Z",(void*)&WB_ClassKnownToNotExist},

test/runtime/memory/ReadVMPageSize.java

+/*
+ * Copyright (c) 2014, 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
+ * @summary Using WhiteBox to get VM page size
+ * @library /testlibrary /testlibrary/whitebox
+ * @build ReadVMPageSize
+ * @run main ClassFileInstaller sun.hotspot.WhiteBox
+ * @run main/othervm  -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI  ReadVMPageSize
+ */
+
+import com.oracle.java.testlibrary.*;
+import sun.hotspot.WhiteBox;
+
+public class ReadVMPageSize {
+  public static void main(String args[]) throws Exception {
+    WhiteBox wb = WhiteBox.getWhiteBox();
+    int pageSize = wb.getVMPageSize();
+    if (pageSize < 0) {
+      throw new Exception("pageSize < 0");
+    } else {
+      System.out.println("Page size = " + pageSize);
+    }
+  }
+}

test/testlibrary/whitebox/sun/hotspot/WhiteBox.java

@@ -75,6 +75,7 @@ public class WhiteBox {
   // Memory
   public native long getObjectAddress(Object o);
   public native int  getHeapOopSize();
+  public native int  getVMPageSize();
   public native boolean isObjectInOldGen(Object o);
   public native long getObjectSize(Object o);