Performance of cache coherence in stackable filing

Stackable design of filing systems constructs sophisticated services from multiple, independently developed layers. This approach has been advocated to address development problems from code re-use, to extensibility, to version management. Individual layers of such a system often need to cache data to improve performance or provide desired functionality. When access to different layers is allowed, cache incoherencies can occur. Without a cache coherence solution, layer designers must either restrict layer access and flexibility or compromise the layered structure to avoid potential data corruption. The value of modular designs such as stacking can be questioned without a suitable solution to this problem. This paper presents a general cache coherence architecture for stackable filing, including a standard approach to data identification as a key component to layered coherence protocols. We also present a detailed performance analysis of one implementation of stack cache-coherence, which suggests that very low overheads can be achieved in practice.