diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 27f3d64d61d..3f6f4c2a3c7 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -41,6 +41,9 @@ Release 2.0.5-beta - UNRELEASED
     HDFS-4525. Provide an API for knowing that whether file is closed or not. 
     (SreeHari via umamahesh)
 
+    HDFS-3940. Add Gset#clear method and clear the block map when namenode is
+    shutdown. (suresh)
+
   OPTIMIZATIONS
 
   BUG FIXES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
index 5fd5a0482dd..b71304cb339 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
@@ -3192,4 +3192,7 @@ assert storedBlock.findDatanode(dn) < 0 : "Block " + block
     OK
   }
 
+  public void shutdown() {
+    blocksMap.close();
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlocksMap.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlocksMap.java
index dbfcaa70138..2f1c06bed6e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlocksMap.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlocksMap.java
@@ -67,7 +67,7 @@ class BlocksMap {
 
 
   void close() {
-    // Empty blocks once GSet#clear is implemented (HDFS-3940)
+    blocks.clear();
   }
 
   BlockCollection getBlockCollection(Block b) {
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java
index 3c79518b622..9587cd970d7 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirectory.java
@@ -2173,4 +2173,8 @@ public class FSDirectory implements Closeable {
       inode.setLocalName(name.getBytes());
     }
   }
+  
+  void shutdown() {
+    nameCache.reset();
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
index e7d9618fefc..ec471b70483 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
@@ -4751,8 +4751,15 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
    * shutdown FSNamesystem
    */
   void shutdown() {
-    if (mbeanName != null)
+    if (mbeanName != null) {
       MBeans.unregister(mbeanName);
+    }
+    if (dir != null) {
+      dir.shutdown();
+    }
+    if (blockManager != null) {
+      blockManager.shutdown();
+    }
   }
   
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSet.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSet.java
index b3de3aac223..f409f5e50f1 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSet.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSet.java
@@ -81,4 +81,6 @@ public interface GSet<K, E extends K> extends Iterable<E> {
     * @throws NullPointerException if key == null.
   */
   E remove(K key);
+
+  void clear();
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSetByHashMap.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSetByHashMap.java
index 7d2c61a7f12..92e49cfc1d5 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSetByHashMap.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/GSetByHashMap.java
@@ -65,4 +65,9 @@ public class GSetByHashMap<K, E extends K> implements GSet<K, E> {
   public Iterator<E> iterator() {
     return m.values().iterator();
   }
+  
+  @Override
+  public void clear() {
+    m.clear();
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/LightWeightGSet.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/LightWeightGSet.java
index 5ab9a8cb355..9919175c72a 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/LightWeightGSet.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/LightWeightGSet.java
@@ -85,7 +85,6 @@ public class LightWeightGSet<K, E extends K> implements GSet<K, E> {
     if (LOG.isDebugEnabled()) {
       LOG.debug("recommended=" + recommended_length + ", actual=" + actual);
     }
-
     entries = new LinkedElement[actual];
     hash_mask = entries.length - 1;
   }
@@ -329,13 +328,18 @@ public class LightWeightGSet<K, E extends K> implements GSet<K, E> {
     final int exponent = e2 < 0? 0: e2 > 30? 30: e2;
     final int c = 1 << exponent;
 
-    if (LightWeightGSet.LOG.isDebugEnabled()) {
-      LOG.debug("Computing capacity for map " + mapName);
-      LOG.debug("VM type       = " + vmBit + "-bit");
-      LOG.debug(percentage + "% max memory = "
-          + StringUtils.TraditionalBinaryPrefix.long2String(maxMemory, "B", 1));
-      LOG.debug("capacity      = 2^" + exponent + " = " + c + " entries");
-    }
+    LOG.info("Computing capacity for map " + mapName);
+    LOG.info("VM type       = " + vmBit + "-bit");
+    LOG.info(percentage + "% max memory = "
+        + StringUtils.TraditionalBinaryPrefix.long2String(maxMemory, "B", 1));
+    LOG.info("capacity      = 2^" + exponent + " = " + c + " entries");
     return c;
   }
+  
+  public void clear() {
+    for (int i = 0; i < entries.length; i++) {
+      entries[i] = null;
+    }
+    size = 0;
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestGSet.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestGSet.java
index 971d538b272..5f43cb53f93 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestGSet.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestGSet.java
@@ -388,6 +388,11 @@ public class TestGSet {
       return String.format(" iterate=%5d, contain=%5d, time elapsed=%5d.%03ds",
           iterate_count, contain_count, t/1000, t%1000);
     }
+
+    @Override
+    public void clear() {
+      gset.clear();
+    }
   }
 
   /** Test data set */