diff --git a/src/share/classes/java/nio/Bits.java b/src/share/classes/java/nio/Bits.java
index 4adf3e48066c663306f6d45a9bc2a1bdab48c5e4..fa11b6be785540f23bd3f8e2b0df9a20e8b03513 100644
--- a/src/share/classes/java/nio/Bits.java
+++ b/src/share/classes/java/nio/Bits.java
@@ -596,6 +596,9 @@ class Bits {                            // package-private
         return pageSize;
     }
 
+    static int pageCount(long size) {
+        return (int)(size + (long)pageSize() - 1L) / pageSize();
+    }
 
     private static boolean unaligned;
     private static boolean unalignedKnown = false;
diff --git a/src/share/classes/java/nio/MappedByteBuffer.java b/src/share/classes/java/nio/MappedByteBuffer.java
index 7e415c67bcaf8bfa22b5e4d65ab556d311455887..4811f41d2e1515deb86f4bfd6409a59fc393e9a4 100644
--- a/src/share/classes/java/nio/MappedByteBuffer.java
+++ b/src/share/classes/java/nio/MappedByteBuffer.java
@@ -25,6 +25,8 @@
 
 package java.nio;
 
+import sun.misc.Unsafe;
+
 
 /**
  * A direct byte buffer whose content is a memory-mapped region of a file.
@@ -93,6 +95,22 @@ public abstract class MappedByteBuffer
             throw new UnsupportedOperationException();
     }
 
+    // Returns the distance (in bytes) of the buffer from the page aligned address
+    // of the mapping. Computed each time to avoid storing in every direct buffer.
+    private long mappingOffset() {
+        int ps = Bits.pageSize();
+        long offset = address % ps;
+        return (offset >= 0) ? offset : (ps + offset);
+    }
+
+    private long mappingAddress(long mappingOffset) {
+        return address - mappingOffset;
+    }
+
+    private long mappingLength(long mappingOffset) {
+        return (long)capacity() + mappingOffset;
+    }
+
     /**
      * Tells whether or not this buffer's content is resident in physical
      * memory.
@@ -115,7 +133,9 @@ public abstract class MappedByteBuffer
         checkMapped();
         if ((address == 0) || (capacity() == 0))
             return true;
-        return isLoaded0(((DirectByteBuffer)this).address(), capacity());
+        long offset = mappingOffset();
+        long length = mappingLength(offset);
+        return isLoaded0(mappingAddress(offset), length, Bits.pageCount(length));
     }
 
     /**
@@ -132,7 +152,20 @@ public abstract class MappedByteBuffer
         checkMapped();
         if ((address == 0) || (capacity() == 0))
             return this;
-        load0(((DirectByteBuffer)this).address(), capacity(), Bits.pageSize());
+        long offset = mappingOffset();
+        long length = mappingLength(offset);
+        load0(mappingAddress(offset), length);
+
+        // touch each page
+        Unsafe unsafe = Unsafe.getUnsafe();
+        int ps = Bits.pageSize();
+        int count = Bits.pageCount(length);
+        long a = mappingAddress(offset);
+        for (int i=0; i<count; i++) {
+            unsafe.getByte(a);
+            a += ps;
+        }
+
         return this;
     }
 
@@ -156,14 +189,15 @@ public abstract class MappedByteBuffer
      */
     public final MappedByteBuffer force() {
         checkMapped();
-        if ((address == 0) || (capacity() == 0))
-            return this;
-        force0(((DirectByteBuffer)this).address(), capacity());
+        if ((address != 0) && (capacity() != 0)) {
+            long offset = mappingOffset();
+            force0(mappingAddress(offset), mappingLength(offset));
+        }
         return this;
     }
 
-    private native boolean isLoaded0(long address, long length);
-    private native int load0(long address, long length, int pageSize);
+    private native boolean isLoaded0(long address, long length, int pageCount);
+    private native void load0(long address, long length);
     private native void force0(long address, long length);
 
 }
diff --git a/src/solaris/native/java/nio/MappedByteBuffer.c b/src/solaris/native/java/nio/MappedByteBuffer.c
index 4a278858677e394ea39083d0a7bcb2d996bdbb52..15c4ec5f5defd02daf7cb43f3e2b53a457892682 100644
--- a/src/solaris/native/java/nio/MappedByteBuffer.c
+++ b/src/solaris/native/java/nio/MappedByteBuffer.c
@@ -32,14 +32,11 @@
 #include <stddef.h>
 #include <stdlib.h>
 
-
 JNIEXPORT jboolean JNICALL
-Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj,
-                                        jlong address, jlong len)
+Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj, jlong address,
+                                         jlong len, jint numPages)
 {
     jboolean loaded = JNI_TRUE;
-    jint pageSize = sysconf(_SC_PAGESIZE);
-    jint numPages = (len + pageSize - 1) / pageSize;
     int result = 0;
     int i = 0;
     void *a = (void *) jlong_to_ptr(address);
@@ -55,9 +52,9 @@ Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj,
     }
 
     result = mincore(a, (size_t)len, vec);
-    if (result != 0) {
-        free(vec);
+    if (result == -1) {
         JNU_ThrowIOExceptionWithLastError(env, "mincore failed");
+        free(vec);
         return JNI_FALSE;
     }
 
@@ -72,23 +69,15 @@ Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj,
 }
 
 
-JNIEXPORT jint JNICALL
+JNIEXPORT void JNICALL
 Java_java_nio_MappedByteBuffer_load0(JNIEnv *env, jobject obj, jlong address,
-                                     jlong len, jint pageSize)
+                                     jlong len)
 {
-    int pageIncrement = pageSize / sizeof(int);
-    int numPages = (len + pageSize - 1) / pageSize;
-    int *ptr = (int *)jlong_to_ptr(address);
-    int i = 0;
-    int j = 0;
-    int result = madvise((caddr_t)ptr, len, MADV_WILLNEED);
-
-    /* touch every page */
-    for (i=0; i<numPages; i++) {
-        j += *((volatile int *)ptr);
-        ptr += pageIncrement;
+    char *a = (char *)jlong_to_ptr(address);
+    int result = madvise((caddr_t)a, (size_t)len, MADV_WILLNEED);
+    if (result == -1) {
+        JNU_ThrowIOExceptionWithLastError(env, "madvise failed");
     }
-    return j;
 }
 
 
@@ -96,13 +85,9 @@ JNIEXPORT void JNICALL
 Java_java_nio_MappedByteBuffer_force0(JNIEnv *env, jobject obj, jlong address,
                                       jlong len)
 {
-    jlong pageSize = sysconf(_SC_PAGESIZE);
-    unsigned long lAddress = address;
-
-    jlong offset = lAddress % pageSize;
-    void *a = (void *) jlong_to_ptr(lAddress - offset);
-    int result = msync(a, (size_t)(len + offset), MS_SYNC);
-    if (result != 0) {
+    void* a = (void *)jlong_to_ptr(address);
+    int result = msync(a, (size_t)len, MS_SYNC);
+    if (result == -1) {
         JNU_ThrowIOExceptionWithLastError(env, "msync failed");
     }
 }
diff --git a/src/windows/native/java/nio/MappedByteBuffer.c b/src/windows/native/java/nio/MappedByteBuffer.c
index 8cce64a26e2b3927746a78b64b7162839dece5a9..5af3b99c73d3c707fe4a42cf27dccb9ae1b9d3d7 100644
--- a/src/windows/native/java/nio/MappedByteBuffer.c
+++ b/src/windows/native/java/nio/MappedByteBuffer.c
@@ -31,8 +31,8 @@
 #include <stdlib.h>
 
 JNIEXPORT jboolean JNICALL
-Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj,
-                                        jlong address, jlong len)
+Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj, jlong address,
+                                         jlong len, jint numPages)
 {
     jboolean loaded = JNI_FALSE;
     /* Information not available?
@@ -43,22 +43,11 @@ Java_java_nio_MappedByteBuffer_isLoaded0(JNIEnv *env, jobject obj,
     return loaded;
 }
 
-JNIEXPORT jint JNICALL
+JNIEXPORT void JNICALL
 Java_java_nio_MappedByteBuffer_load0(JNIEnv *env, jobject obj, jlong address,
-                                     jlong len, jint pageSize)
+                                     jlong len)
 {
-    int *ptr = (int *) jlong_to_ptr(address);
-    int pageIncrement = pageSize / sizeof(int);
-    jlong numPages = (len + pageSize - 1) / pageSize;
-    int i = 0;
-    int j = 0;
-
-    /* touch every page */
-    for (i=0; i<numPages; i++) {
-        j += *((volatile int *)ptr);
-        ptr += pageIncrement;
-    }
-    return j;
+    // no madvise available
 }
 
 JNIEXPORT void JNICALL
diff --git a/test/java/nio/MappedByteBuffer/Basic.java b/test/java/nio/MappedByteBuffer/Basic.java
index 5b56918c5633be081ff3eeec0ae01ea7bf1df56c..3b068b7698394cc4d920cd8558abe85d48279ba0 100644
--- a/test/java/nio/MappedByteBuffer/Basic.java
+++ b/test/java/nio/MappedByteBuffer/Basic.java
@@ -22,7 +22,7 @@
  */
 
 /* @test
- * @bug 4462336
+ * @bug 4462336 6799037
  * @summary Simple MappedByteBuffer tests
  * @run main/othervm Basic
  */
@@ -52,6 +52,12 @@ public class Basic {
         mbb.force();
         if (!mbb.isReadOnly())
             throw new RuntimeException("Incorrect isReadOnly");
+
+        // repeat with unaligned position in file
+        mbb = fc.map(FileChannel.MapMode.READ_ONLY, 1, 10);
+        mbb.load();
+        mbb.isLoaded();
+        mbb.force();
         fc.close();
         fis.close();
 
diff --git a/test/java/nio/MappedByteBuffer/Truncate.java b/test/java/nio/MappedByteBuffer/Truncate.java
new file mode 100644
index 0000000000000000000000000000000000000000..09dee07e60cc64fb6346ce5ba614f514f2fbc669
--- /dev/null
+++ b/test/java/nio/MappedByteBuffer/Truncate.java
@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2010, 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
+ * @bug 6934977
+ * @summary Test MappedByteBuffer operations after mapped bye buffer becomes
+ *   inaccessible
+ * @run main/othervm Truncate
+ */
+
+import java.io.*;
+import java.nio.*;
+import java.nio.channels.*;
+import java.util.concurrent.Callable;
+
+public class Truncate {
+
+    static final long INITIAL_FILE_SIZE   = 32000L;
+    static final long TRUNCATED_FILE_SIZE =   512L;
+
+    public static void main(String[] args) throws Exception {
+        File blah = File.createTempFile("blah", null);
+        blah.deleteOnExit();
+
+        final FileChannel fc = new RandomAccessFile(blah, "rw").getChannel();
+        fc.position(INITIAL_FILE_SIZE).write(ByteBuffer.wrap("THE END".getBytes()));
+        final MappedByteBuffer mbb =
+            fc.map(FileChannel.MapMode.READ_WRITE, 0, fc.size());
+        boolean truncated;
+        try {
+            fc.truncate(TRUNCATED_FILE_SIZE);
+            truncated = true;
+        } catch (IOException ioe) {
+            // probably on Windows where a file cannot be truncated when
+            // there is a file mapping.
+            truncated = false;
+        }
+        if (truncated) {
+            // Test 1: access region that is no longer accessible
+            execute(new Callable<Void>() {
+                public Void call() {
+                    mbb.get((int)TRUNCATED_FILE_SIZE + 1);
+                    mbb.put((int)TRUNCATED_FILE_SIZE + 2, (byte)123);
+                    return null;
+                }
+            });
+            // Test 2: load buffer into memory
+            execute(new Callable<Void>() {
+                public Void call() throws IOException {
+                    mbb.load();
+                    return null;
+                }
+            });
+        }
+        fc.close();
+    }
+
+    // Runs the given task in its own thread. If operating correcting the
+    // the thread will terminate with an InternalError as the mapped buffer
+    // is inaccessible.
+    static void execute(final Callable<?> c) {
+        Runnable r = new Runnable() {
+            public void run() {
+                try {
+                    Object ignore = c.call();
+                } catch (Exception ignore) {
+                }
+            }
+        };
+        Thread t = new Thread(r);
+        t.start();
+        try { t.join(); } catch (InterruptedException ignore) { }
+    }
+}