HDFS-8773. Few FSNamesystem metrics are not documented in the Metrics page. Contributed by Rakesh R.

(cherry picked from commit a26cc66f38daec2342215a66b599bf59cee1112c)

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

hadoop-common-project/hadoop-common/src/site/markdown/Metrics.md

@@ -230,6 +230,11 @@ Each metrics record contains tags such as HAState and Hostname as additional inf
 | `BlockCapacity` | Current number of block capacity |
 | `StaleDataNodes` | Current number of DataNodes marked stale due to delayed heartbeat |
 | `TotalFiles` | Current number of files and directories (same as FilesTotal) |
+| `MissingReplOneBlocks` | Current number of missing blocks with replication factor 1 |
+| `NumFilesUnderConstruction` | Current number of files under construction |
+| `NumActiveClients` | Current number of active clients holding lease |
+| `HAState` | (HA-only) Current state of the NameNode: initializing or active or standby or stopping state |
+| `FSState` | Current state of the file system: Safemode or Operational |
 
 JournalNode
 -----------

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

@@ -721,6 +721,10 @@ Release 2.8.0 - UNRELEASED
 
     HDFS-7582. Enforce maximum number of ACL entries separately per access
     and default. (vinayakumarb)
+
+    HDFS-8773. Few FSNamesystem metrics are not documented in the Metrics page.
+    (Rakesh R via cnauroth)
+
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES