address the comments

core/src/main/scala/org/apache/spark/deploy/ApplicationDescription.scala

@@ -44,7 +44,7 @@ private[spark] class ApplicationDescription(
       name, maxCores, memoryPerSlave, command, appUiUrl, eventLogDir, eventLogCodec)
 
   // only valid when spark.executor.multiPerWorker is set to true
-  var maxCorePerExecutor = maxCores
+  var maxCorePerExecutor = None
 
   override def toString: String = "ApplicationDescription(" + name + ")"
 }

core/src/main/scala/org/apache/spark/deploy/master/Master.scala

@@ -609,7 +609,9 @@ private[master] class Master(
         var leftExecutorNumToAssign = usableWorkers.map(_.memoryFree / memoryPerExecutor).sum
         var maxCoresLeft = app.coresLeft
         val numUsable = usableWorkers.length
-        // 2D array to track the number of cores of each executor assigned to each worker
+        // A 2D array that tracks the number of cores used by each executor launched on
+        // each worker. The first index refers to the usable worker, and the second index
+        // refers to the executor launched on that worker.
         val assigned = Array.fill[ListBuffer[Int]](numUsable)(new ListBuffer[Int])
         val assignedSum = Array.fill[Int](numUsable)(0)
         var pos = 0

core/src/main/scala/org/apache/spark/deploy/master/ui/ApplicationPage.scala

@@ -83,14 +83,14 @@ private[ui] class ApplicationPage(parent: MasterWebUI) extends WebUIPage("app")
             <li><strong>Name:</strong> {app.desc.name}</li>
             <li><strong>User:</strong> {app.desc.user}</li>
             <li><strong>Cores:</strong>
-              {
+            {
               if (app.desc.maxCores.isEmpty) {
                 "Unlimited (%s granted)".format(app.coresGranted)
               } else {
                 "%s (%s granted, %s left)".format(
                   app.desc.maxCores.get, app.coresGranted, app.coresLeft)
               }
-              }
+            }
             </li>
             <li>
               <strong>Executor Memory:</strong>

docs/configuration.md

@@ -103,6 +103,7 @@ of the most common options to set are:
     Number of cores to use for the driver process, only in cluster mode.
   </td>
 </tr>
+<tr>
   <td><code>spark.driver.maxResultSize</code></td>
   <td>1g</td>
   <td>
@@ -127,6 +128,14 @@ of the most common options to set are:
     or in your default properties file.
   </td>
 </tr>
+<tr>
+  <td>spark.executor.maxCoreNumPerExecutor</td>
+  <td>1</td>
+  <td>
+    set the max number of cores assigned to each executor; this property is only valid when
+    <code>spark.executor.multiPerWorker</code> is set to true.
+  </td>
+</tr>
 <tr>
   <td><code>spark.executor.memory</code></td>
   <td>512m</td>
@@ -1255,25 +1264,6 @@ Apart from these, the following properties are also available, and may be useful
 <tr>
   <td><code>spark.ui.view.acls</code></td>
   <td>Empty</td>
-</tr>
-<tr>
-  <td>spark.executor.multiPerWorker</td>
-  <td>false</td>
-  <td>
-    enable user to run multiple executors in the same worker.
-  </td>
-</tr>
-<tr>
-  <td>spark.executor.maxCoreNumPerExecutor</td>
-  <td>1</td>
-  <td>
-    set the max number of cores assigned to each executor; this property is only valid when
-    <code>spark.executor.multiPerWorker</code> is set to true.
-  </td>
-</tr>
-<tr>
-  <td>spark.executor.extraClassPath</td>
-  <td>(none)</td>
   <td>
     Comma separated list of users that have view access to the Spark web ui. By default only the
     user that started the Spark job has view access.