improve javadocs

core/src/main/java/org/elasticsearch/search/suggest/completion/CompletionFieldStats.java

@@ -35,7 +35,7 @@ import java.io.IOException;
 public class CompletionFieldStats {
 
     /**
-     * Returns total in-heap bytes used by all suggesters.  This method is <code>O(numIndexedFields)</code>.
+     * Returns total in-heap bytes used by all suggesters.  This method has CPU cost <code>O(numIndexedFields)</code>.
      *
      * @param fieldNamePatterns if non-null, any completion field name matching any of these patterns will break out its in-heap bytes
      * separately in the returned {@link CompletionStats}