HDFS-7570. SecondaryNameNode need twice memory when calling reloadFromImageFile. Contributed by zhaoyunjiong.

(cherry picked from commit 85aec75ce53445e1abf840076d2e10f1e3c6d69b)
(cherry picked from commit 27eecaef10feb49c4160ad289fd301bba6608973)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -169,6 +169,9 @@ Release 2.6.1 - UNRELEASED
     HDFS-8846. Add a unit test for INotify functionality across a layout
     version upgrade (Zhe Zhang via Colin P. McCabe)
 
+    HDFS-7470. SecondaryNameNode need twice memory when calling
+    reloadFromImageFile. (zhaoyunjiong via cnauroth)
+
 Release 2.6.0 - 2014-11-18
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java

@@ -3811,4 +3811,9 @@ public class BlockManager {
     stopReplicationInitializer();
     blocksMap.close();
   }
+  
+  public void clear() {
+    clearQueues();
+    blocksMap.clear();
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlocksMap.java

@@ -85,9 +85,13 @@ class BlocksMap {
 
 
   void close() {
+    clear();
+    blocks = null;
+  }
+  
+  void clear() {
     if (blocks != null) {
       blocks.clear();
-      blocks = null;
     }
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -651,6 +651,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
     snapshotManager.clearSnapshottableDirs();
     cacheManager.clear();
     setImageLoaded(false);
+    blockManager.clear();
   }
 
   @VisibleForTesting