[GitHub] [flink] 1996fanrui commented on a diff in pull request #22381: [FLINK-31763][runtime] Ensure that the total number of requested buffers does not exceed poolSize + maxOverdraftBuffersPerGate

["1996fanrui (via GitHub)" <gi...@apache.org>]

1996fanrui commented on code in PR #22381:
URL: https://github.com/apache/flink/pull/22381#discussion_r1163988392


##########
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/buffer/LocalBufferPool.java:
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@@ -671,13 +675,20 @@ public void setNumBuffers(int numBuffers) {
 
             currentPoolSize = Math.min(numBuffers, maxNumberOfMemorySegments);
 
-            // reset overdraft buffers
+            // If pool size increases, try to convert overdraft buffer to ordinary buffer.
             while (numberOfRequestedOverdraftMemorySegments > 0
                     && numberOfRequestedMemorySegments < currentPoolSize) {
                 numberOfRequestedOverdraftMemorySegments--;
                 numberOfRequestedMemorySegments++;
             }
 
+            // If pool size decreases, try to convert ordinary buffer to overdraft buffer.
+            while (numberOfRequestedMemorySegments > currentPoolSize
+                    && numberOfRequestedOverdraftMemorySegments < maxOverdraftBuffersPerGate) {
+                numberOfRequestedMemorySegments--;
+                numberOfRequestedOverdraftMemorySegments++;
+            }

Review Comment:
   Hi @reswqa , thanks for the fix.
   
   I'm curious, what's wrong with just leaving `numberOfRequestedMemorySegments > currentPoolSize`? Count extra buffers to the `overdraft buffer`.
   
   ```suggestion
               while (numberOfRequestedMemorySegments > currentPoolSize) {
                   numberOfRequestedMemorySegments--;
                   numberOfRequestedOverdraftMemorySegments++;
               }
   ```



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