Editing Page replacement algorithm (section)

====Variants of clock====
* GCLOCK: Generalized clock page replacement algorithm.<ref>{{cite journal|last1=Smith|first1=Alan Jay|title=Sequentiality and prefetching in database systems|journal=ACM Transactions on Database Systems|volume=3|issue=3|pages=223–247|date=September 1978|doi=10.1145/320263.320276|publisher=ACM|language=en|location=New York, NY, USA|s2cid=11611563|doi-access=free}}</ref>
* Clock-Pro keeps a circular list of information about recently referenced pages, including all M pages in memory as well as the most recent M pages that have been paged out. This extra information on paged-out pages, like the similar information maintained by [[adaptive replacement cache|ARC]], helps it work better than LRU on large loops and one-time scans.<ref>{{cite conference |first2=Feng |last2=Chen |url=http://www.cse.ohio-state.edu/hpcs/WWW/HTML/publications/papers/TR-05-3.pdf |title=CLOCK-Pro: an effective improvement of the CLOCK replacement |first3=Xiaodong |last3=Zhang |first1=Song |last1=Jiang |date=10-15 April 2005 |conference=2005 USENIX Annual Technical Conference |conference-url=https://www.usenix.org/conference/2005usenixannualtechnicalconference |publisher=USENIX Association |archive-url=http://archive.wikiwix.com/cache/20190612095142/http://www.cse.ohio-state.edu/hpcs/WWW/HTML/publications/papers/TR-05-3.pdf |archive-date=12 June 2019 |location=Anaheim, CA, USA |page=35 |url-status=live |language=en |access-date=24 March 2009 }}</ref>
* WSclock.<ref>{{cite conference |first2=John L. |last2=Hennessy |url=http://infolab.stanford.edu/~manku/quals/zpapers/81-wsclock.pdf.gz |title=WSCLOCK—a simple and effective algorithm for virtual memory management |format=gzipped PDF |first1=Richard W. |last1=Carr |date=14-16 December 1981 |conference=Eighth ACM symposium on Operating systems principles |conference-url=https://dl.acm.org/citation.cfm?doid=800216 |publisher=ACM |archive-url=https://web.archive.org/web/20070610070838/http://infolab.stanford.edu/~manku/quals/zpapers/81-wsclock.pdf.gz |archive-date=10 June 2007 |location=Pacific Grove, CA, USA |pages=87–95 |url-status=live |language=en |isbn=0-89791-062-1 |doi=10.1145/800216.806596}}</ref> By combining the Clock algorithm with the concept of a working set (i.e., the set of pages expected to be used by that process during some time interval), the performance of the algorithm can be improved. In practice, the "aging" algorithm and the "WSClock" algorithm are probably the most important page replacement algorithms.<ref>{{cite web|last1=Gottlieb|first1=Allan|title=WSClock|url=http://www.cs.nyu.edu/courses/spring09/V22.0202-002/wsclock-davis.html|website=New York University Computer Science Department|access-date=12 June 2019|archive-url=https://archive.today/20120730042750/http://www.cs.nyu.edu/courses/spring09/V22.0202-002/wsclock-davis.html|archive-date=30 July 2012|url-status=live}}</ref><ref>{{cite web|last1=Tanenbaum|first1=Andrew S.|title=Page Replacement Algorithms|url=http://www.informit.com/articles/article.aspx?p=25260&seqNum=11|website=InformIT|access-date=12 June 2019|archive-url=https://archive.today/20120910015221/http://www.informit.com/articles/article.aspx?p=25260&seqNum=11|archive-date=10 September 2012|url-status=live}}</ref>
* Clock with Adaptive Replacement (CAR) is a page replacement algorithm that has performance comparable to [[Adaptive replacement cache|ARC]], and substantially outperforms both LRU and CLOCK.<ref>{{cite conference |first2=Dharmendra S. |last2=Modha |name-list-style=amp |url=http://usenix.org/publications/library/proceedings/fast04/tech/full_papers/bansal/bansal.pdf |title=CAR: Clock with Adaptive Replacement |first1=Sorav |last1=Bansal |date=31 March – 2 April 2004 |conference=3rd USENIX Conference on File and Storage Technologies (FAST '04) |conference-url=https://www.usenix.org/conference/fast04 |publisher=USENIX Association |archive-url=https://web.archive.org/web/20040731112559/http://www.almaden.ibm.com/cs/people/dmodha/clockfast.pdf |archive-date=31 July 2004| url-status=live |location=San Francisco, CA, USA |pages=187–200 |language=en |citeseerx=10.1.1.105.6057}}</ref> The algorithm CAR is self-tuning and requires no user-specified magic parameters.

CLOCK is a conservative algorithm, so it is <math> \tfrac{k}{k-h+1}</math>-competitive.