Structuring operating system aspects.

Key elements of operating systems crosscut – their implementation is inherently coupled with several layers of the system. Prefetching, for example, is a critical architectural performance optimization that amortizes the cost of going to disk by predicting and retrieving additional data with each explicit disk request. The implementation of prefetching, however, is tightly coupled with both high-level context of the request source and low-level costs of additional retrieval. In a traditional OS implementation, small clusters of customized prefetching code appear at both high and low levels along most execution paths that involve going to disk. This makes prefetching difficult to reason about and change, and interferes with the clarity of the primary functionality within which prefetching is embedded.