MAPREDUCE-6063. Correct spill size calculation for spills wrapping the circular buffer. Contributed by zhihai xu.

hadoop-mapreduce-project/CHANGES.txt

@@ -267,6 +267,9 @@ Release 2.6.0 - UNRELEASED
     MAPREDUCE-5931. Validate SleepJob command line parameters (Gera Shegalov
     via jlowe)
 
+    MAPREDUCE-6063. Correct spill size calculation for spills wrapping the
+    circular buffer. (zhihai xu via cdouglas)
+
 Release 2.5.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/MapTask.java

@@ -1575,9 +1575,7 @@ public class MapTask extends Task {
                                        InterruptedException {
       //approximate the length of the output file to be the length of the
       //buffer + header lengths for the partitions
-      final long size = (bufend >= bufstart
-          ? bufend - bufstart
-          : (bufvoid - bufend) + bufstart) +
+      final long size = distanceTo(bufstart, bufend, bufvoid) +
                   partitions * APPROX_HEADER_LENGTH;
       FSDataOutputStream out = null;
       try {