Once the ULC flusher has finished flushing the ULC pages into the log cache, it queues the task request into a wakeup queue. The log writer patrols the dirty buffer chain in the log cache, issuing a write command if it finds dirty buffers, and monitors the wakeup queue for tasks whose pages are all written to disk. Since the log writer patrols the dirty buffer chain, it knows when a buffer is ready to write to disk.
