diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/MRAppMaster.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/MRAppMaster.java
index dfde6b4227..69bc60f557 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/MRAppMaster.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/MRAppMaster.java
@@ -1676,6 +1676,7 @@ public static void main(String[] args) {
       ShutdownHookManager.get().addShutdownHook(
         new MRAppMasterShutdownHook(appMaster), SHUTDOWN_HOOK_PRIORITY);
       JobConf conf = new JobConf(new YarnConfiguration());
+      // 加载job.xml信息
       conf.addResource(new Path(MRJobConfig.JOB_CONF_FILE));
       
       MRWebAppUtil.initialize(conf);
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/commit/CommitterEventHandler.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/commit/CommitterEventHandler.java
index c72e13e648..9b3abe54d3 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/commit/CommitterEventHandler.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/commit/CommitterEventHandler.java
@@ -252,6 +252,7 @@ public void run() {
     @SuppressWarnings("unchecked")
     protected void handleJobSetup(CommitterJobSetupEvent event) {
       try {
+        // 主要是创建attempt路径
         committer.setupJob(event.getJobContext());
         context.getEventHandler().handle(
             new JobSetupCompletedEvent(event.getJobID()));
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/job/impl/JobImpl.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/job/impl/JobImpl.java
index 290b4a240f..5ca306b6fe 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/job/impl/JobImpl.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/job/impl/JobImpl.java
@@ -1455,6 +1455,7 @@ public JobStateInternal transition(JobImpl job, JobEvent event) {
       }
       
       try {
+        // 初始化token等信息。
         setup(job);
         job.fs = job.getFileSystem(job.conf);