HDFS-17112. Show decommission duration in JMX and HTML. (#5866). Contributed by Shuyan Zhang.

Reviewed-by: hfutatzhanghb <1036798979@qq.com>
Reviewed-by: Tao Li <tomscut@apache.org>
Signed-off-by: He Xiaoqiao <hexiaoqiao@apache.org>

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

@@ -6664,6 +6664,8 @@ public String getDecomNodes() {
           node.getLeavingServiceStatus().getOutOfServiceOnlyReplicas())
           .put("underReplicateInOpenFiles",
           node.getLeavingServiceStatus().getUnderReplicatedInOpenFiles())
+          .put("decommissionDuration",
+              monotonicNow() - node.getLeavingServiceStatus().getStartTime())
           .build();
       info.put(node.getXferAddrWithHostname(), innerinfo);
     }

hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/hdfs/dfshealth.html

@@ -406,6 +406,7 @@
       <th>Under replicated blocks</th>
       <th>Blocks with no live replicas</th>
       <th>Under Replicated Blocks <br/>In files under construction</th>
+      <th>Decommission duration</th>
     </tr>
   </thead>
   {#DecomNodes}
@@ -414,6 +415,7 @@
     <td>{underReplicatedBlocks}</td>
     <td>{decommissionOnlyReplicas}</td>
     <td>{underReplicateInOpenFiles}</td>
+    <td>{decommissionDuration}ms</td>
   </tr>
   {/DecomNodes}
 </table>