Hexiaoqiao commented on code in PR #8463:
URL: https://github.com/apache/hadoop/pull/8463#discussion_r3245949619


##########
hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java:
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@@ -1230,7 +1230,9 @@ void actualGetFromOneDataNode(final DNAddrPair datanode, 
final long startInBlk,
         long beginReadMS = Time.monotonicNow();
         int nread = 0;
         int ret;
-        while (true) {
+        // Stop once the slice is filled; an extra read with remaining()==0
+        // can trigger wasted slow-lane I/O in SCR.
+        while (tmp.hasRemaining()) {

Review Comment:
   Great catch. Make sense to me.
   Just wonder how you hit this corner case, and why `tmp.hasRemaining==0` here?



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