HDFS-10900. DiskBalancer: Complete the documents for the report command. Contributed by Yiqun Lin.

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSCommands.md

@@ -445,6 +445,8 @@ Usage:
          [-query <datanode>]
          [-cancel <planfile>]
          [-cancel <planID> -node <datanode>]
+         [-report -node [<DataNodeID|IP|Hostname>,...]]
+         [-report -node -top <topnum>]
 
 | COMMAND\_OPTION | Description |
 |:---- |:---- |
@@ -452,7 +454,7 @@ Usage:
 |-execute| Executes a given plan on a datanode|
 |-query| Gets the current diskbalancer status from a datanode|
 |-cancel| Cancels a running plan|
-
+|-report| Reports the volume information from datanode(s)|
 
 Runs the diskbalancer CLI. See [HDFS Diskbalancer](./HDFSDiskbalancer.html) for more information on this command.
 

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSDiskbalancer.md

@@ -106,10 +106,13 @@ or
 Plan ID can be read from datanode using query command.
 
 ### Report
-Report command provides detailed report about node(s).
+Report command provides detailed report of specified node(s) or top nodes that will benefit from running disk balancer.
 
 `hdfs diskbalancer -fs http://namenode.uri -report -node [<DataNodeID|IP|Hostname>,...]`
 
+or
+
+`hdfs diskbalancer -fs http://namenode.uri -report -top topnum`
 
 Settings
 --------