 Buffer cache writeback

Transferring a dirty buffer's current contents to its backing location. The buffer cache state model permits no concurrent modification during the transfer and marks the result clean only after successful completion. A failed write preserves the obligation and prevents the proposed buffer cache eviction. A production implementation allowing new writes during input-output must retain their obligation rather than incorrectly clearing it when an older transfer finishes.

A successful transfer can leave data in a device's volatile memory cache. A storage flush or the documented equivalent supplies a persistence boundary; file-system journaling supplies recovery rules for related updates. These are additional obligations, not consequences of becoming a clean buffer.^[ref]