A few mechanics in worker.py are very well self-contained, and it would make a lot of sense to encapsulate them into a separate module/class in order to reduce complexity:

• memory limit and thresholds
• initialisation of the SpillBuffer
• memory_monitor(), which handles pause, unpause, and force evict from spillbuffer

From the Worker's perspective, Worker.data should be treated as an opaque MutableMapping.

This is just a refactoring, with no functional impact.

Consider deprecating init arguments to Worker using target, spill, pause threshold etc. in favour of dask.config.

This change is part of the wider epic

• (Worker) State Machine determinism and replayability #5736

Related issues:

• Create MutableMapping for automatic compression #3656
• Asynchronous Disk Access in Workers #4424
• Thoughts on additional spilling layers #4629
• Change the memory-limit on the fly #5367
• Deserialise data on demand #5900