clock-pro · research · also CLOCK-Pro replacement

CLOCK-Pro

CLOCK-Pro is an adaptive page-replacement policy combining CLOCK reference bits with bounded history of evicted pages.

Three hands manage hot pages, resident cold victims and cold-page test periods. Eviction can discard a cold page's data while retaining its metadata for a later reuse test. A nonresident history match still requires a page fetch. [1]

The cold-page target increases after reuse within a test period and decreases when a test expires without reuse; these observations include resident and nonresident cold pages. [1]

Relations

related

CLOCK cache replacement, Ghost cache entry, Cache pollution, Adaptive Replacement Cache

Advantages

• Retained history lets replacement react to reuse after eviction. [1]

Limitations

• The historical Linux 2.4.21 prototype does not establish present-day implementation behavior or universal speedups. [1]

Citations

1. Song Jiang, Feng Chen and Xiaodong Zhang. CLOCK-Pro: An Effective Improvement of the CLOCK Replacement. USENIX ATC 2005, sections 4.2-4.4 and 5.2. (accessed 2026-10-24)

Further reading

2. Hesela: cache-history matches versus resident hits. (accessed 2026-10-24)

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