Github user zhijiangW commented on the issue:
https://github.com/apache/flink/pull/4533
`notifyCreditAvailable` would be called by three logics in
`RemoteInputChannel`. They are `RemoteInputChannel#recycle`,
`RemoteInputChannel#notifyBufferAvailable` and
`RemoteInputChannel#onSenderBacklog` which are covered in previous PRs.
All the previous PRs are already merged into master except
[FLINK-7406](https://github.com/apache/flink/pull/4509).
In details, when the channel's credit is increased from zero, it will try
to notify the producer of it. For example:
1. Recycle the exclusive buffers to increase credit after record processed.
2. The buffer pool notifies the channel of available floating buffers to
increase credit
3. When receiving the backlog from producer, it may trigger to request
floating buffers from buffer pool. Credit is increased when returned floating
buffers from buffer pool.
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