Editing Cache replacement policies (section)

===== {{anchor|CLOCK-Pro}}Clock-Pro =====
The LRU algorithm cannot be implemented in the critical path of computer systems, such as [[operating system]]s, due to its high overhead; [[Page replacement algorithm#Clock|Clock]], an approximation of LRU, is commonly used instead. Clock-Pro is an approximation of [[LIRS caching algorithm|LIRS]] for low-cost implementation in systems.<ref>{{cite journal |last1=Jiang |first1=Song |last2=Chen |first2=Feng |last3=Zhang |first3=Xiaodong |date=2005 |title=CLOCK-Pro: An Effective Improvement of the CLOCK Replacement |url=http://web.cse.ohio-state.edu/hpcs/WWW/HTML/publications/papers/TR-05-3.pdf |journal=Proceedings of the Annual Conference on USENIX Annual Technical Conference |publisher=USENIX Association |pages=323–336}}</ref> Clock-Pro has the basic Clock framework, with three advantages. It has three "clock hands" (unlike Clock's single "hand"), and can approximately measure the reuse distance of data accesses. Like LIRS, it can quickly evict one-time-access or low-[[Locality of reference|locality]] data items. Clock-Pro is as complex as Clock, and is easy to implement at low cost. The buffer-cache replacement implementation in the 2017 version of [[Linux]] combines LRU and Clock-Pro.<ref>{{cite web |date=2017-12-30 |title=Linux Memory Management: Page Replacement Design. |url=https://linux-mm.org/PageReplacementDesign |access-date=2020-06-30}}</ref><ref>{{cite web |date=2005-08-16 |title=A CLOCK-Pro page replacement implementation |url=https://lwn.net/Articles/147879/ |access-date=2020-06-30 |publisher=[[LWN.net]]}}</ref>