[Minor] Fixes on top of apache#1679

Minor fixes on top of apache#1679.

Author: Andrew Or <andrewor14@gmail.com>

Closes apache#1736 from andrewor14/amend-#1679 and squashes the following commits:

3b46f5e [Andrew Or] Minor fixes

core/src/main/scala/org/apache/spark/storage/BlockManagerSource.scala

@@ -46,9 +46,8 @@ private[spark] class BlockManagerSource(val blockManager: BlockManager, sc: Spar
   metricRegistry.register(MetricRegistry.name("memory", "memUsed_MB"), new Gauge[Long] {
     override def getValue: Long = {
       val storageStatusList = blockManager.master.getStorageStatus
-      val maxMem = storageStatusList.map(_.maxMem).sum
-      val remainingMem = storageStatusList.map(_.memRemaining).sum
-      (maxMem - remainingMem) / 1024 / 1024
+      val memUsed = storageStatusList.map(_.memUsed).sum
+      memUsed / 1024 / 1024
     }
   })
 

core/src/main/scala/org/apache/spark/storage/StorageUtils.scala

@@ -172,16 +172,13 @@ class StorageStatus(val blockManagerId: BlockManagerId, val maxMem: Long) {
   def memRemaining: Long = maxMem - memUsed
 
   /** Return the memory used by this block manager. */
-  def memUsed: Long =
-    _nonRddStorageInfo._1 + _rddBlocks.keys.toSeq.map(memUsedByRdd).sum
+  def memUsed: Long = _nonRddStorageInfo._1 + _rddBlocks.keys.toSeq.map(memUsedByRdd).sum
 
   /** Return the disk space used by this block manager. */
-  def diskUsed: Long =
-    _nonRddStorageInfo._2 + _rddBlocks.keys.toSeq.map(diskUsedByRdd).sum
+  def diskUsed: Long = _nonRddStorageInfo._2 + _rddBlocks.keys.toSeq.map(diskUsedByRdd).sum
 
   /** Return the off-heap space used by this block manager. */
-  def offHeapUsed: Long =
-    _nonRddStorageInfo._3 + _rddBlocks.keys.toSeq.map(offHeapUsedByRdd).sum
+  def offHeapUsed: Long = _nonRddStorageInfo._3 + _rddBlocks.keys.toSeq.map(offHeapUsedByRdd).sum
 
   /** Return the memory used by the given RDD in this block manager in O(1) time. */
   def memUsedByRdd(rddId: Int): Long = _rddStorageInfo.get(rddId).map(_._1).getOrElse(0L)
@@ -246,7 +243,7 @@ private[spark] object StorageUtils {
       val rddId = rddInfo.id
       // Assume all blocks belonging to the same RDD have the same storage level
       val storageLevel = statuses
-        .map(_.rddStorageLevel(rddId)).flatMap(s => s).headOption.getOrElse(StorageLevel.NONE)
+        .flatMap(_.rddStorageLevel(rddId)).headOption.getOrElse(StorageLevel.NONE)
       val numCachedPartitions = statuses.map(_.numRddBlocksById(rddId)).sum
       val memSize = statuses.map(_.memUsedByRdd(rddId)).sum
       val diskSize = statuses.map(_.diskUsedByRdd(rddId)).sum