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

(cherry picked from commit 85aec75ce53445e1abf840076d2e10f1e3c6d69b)

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

@@ -427,6 +427,9 @@ Release 2.7.0 - UNRELEASED
     HDFS-5445. PacketReceiver populates the packetLen field in PacketHeader
     incorrectly (Jonathan Mace via Colin P. McCabe)
 
+    HDFS-7470. SecondaryNameNode need twice memory when calling
+    reloadFromImageFile. (zhaoyunjiong via cnauroth)
+
 Release 2.6.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

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

@@ -3743,4 +3743,9 @@ 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

@@ -86,9 +86,13 @@ 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

@@ -585,6 +585,7 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     snapshotManager.clearSnapshottableDirs();
     cacheManager.clear();
     setImageLoaded(false);
+    blockManager.clear();
   }
 
   @VisibleForTesting