登录查看更多内容

Last updated on 2024年8月25日

How do you implement the LRU algorithm for page replacement?

由人工智能和领英社区提供技术支持

Page replacement is a technique used by operating systems to manage the limited physical memory available for running processes. When a process requests a page that is not in memory, the operating system has to swap out an existing page to make room for the new one. The question is, which page should be swapped out? One of the most popular algorithms for this decision is the least recently used (LRU) algorithm, which selects the page that has not been accessed for the longest time. In this article, you will learn how to implement the LRU algorithm for page replacement in a simple and efficient way.

此文章中的业界达人

由社区从 10 条内容中精选。了解更多

Pedro Abreu .'.

1 What is LRU?

LRU stands for least recently used, and it is based on the assumption that the pages that have been used recently are more likely to be used again in the near future. Therefore, the LRU algorithm keeps track of the order of page accesses and swaps out the page that has been accessed the least recently. This way, it tries to minimize the number of page faults, which occur when a process requests a page that is not in memory and causes a disk access.

添加您的观点

Pedro Abreu .'.
举报内容
Em resumo, um LRU é uma unidade funcional completa que pode ser substituída no nível de campo para restaurar o item final a uma condi??o operacional pronta. Ele desempenha um papel importante na manuten??o e logística de sistemas complexos.

已翻译

赞
Thiago Goes

Engenheiro Metalurgista | Master Black Belt | Gestor Ambiental | Gestor de Dados | Técnico em Minera??o | Técnico em Seguran?a do Trabalho
举报内容
O algoritmo LRU (Least Recently Used) é uma técnica de substitui??o de página em sistemas de gerenciamento de memória virtual. Ele prioriza a remo??o da página que n?o foi utilizada por mais tempo, mantendo um registro do histórico de acessos. A implementa??o geralmente envolve o uso de estruturas de dados, como listas ou contadores, para rastrear a ordem de acesso às páginas. A página menos recentemente utilizada é escolhida para ser substituída quando necessário, otimizando o uso da memória virtual.

已翻译

赞

2 How to track page accesses?

One way to track the order of page accesses is to use a linked list, where each node represents a page and its position in the list indicates its recency. The most recently accessed page is at the head of the list, and the least recently accessed page is at the tail of the list. Whenever a page is accessed, it is moved to the head of the list. Whenever a page needs to be swapped out, it is removed from the tail of the list. This way, the list always reflects the LRU order of the pages.

添加您的观点

Pedro Abreu .'.
举报内容
Rastrear e analisar os acessos de um site é fundamental para compreender o comportamento dos usuários, identificar tendências e tomar decis?es estratégicas. Aqui est?o algumas abordagens e ferramentas para realizar esse monitoramento

已翻译

赞
Thiago Goes

Engenheiro Metalurgista | Master Black Belt | Gestor Ambiental | Gestor de Dados | Técnico em Minera??o | Técnico em Seguran?a do Trabalho
举报内容
Rastrear acessos à página para o algoritmo LRU pode ser feito usando listas ou contadores. Com listas, mantenha a ordem de acesso e substitua a página menos recentemente usada no final. Com contadores, atribua a cada página um contador atualizado a cada acesso e substitua aquela com o menor contador quando necessário.

已翻译

赞

3 How to implement LRU with a linked list?

To implement the LRU algorithm with a linked list, you will need two data structures: a hash map and a doubly linked list. The hash map maps each page number to its corresponding node in the linked list and the doubly linked list maintains the LRU order of the pages. When a page is requested, it is checked if it is in the hash map. If it is, it is moved to the head of the linked list. If it is not, a page fault occurs and a page needs to be swapped out. To swap out a page, check if the linked list is full. If it is, remove the tail node from the list and delete its entry from the hash map. If not, add a new node to the head of the list and insert its entry to the hash map. In either case, update both the head pointer of the linked list and the hash map entry of the new page to point to the new node. Reporting and documenting this incident helps inform and reassure stakeholders while providing valuable insights for improving cloud security posture.

添加您的观点

Pedro Abreu .'.
举报内容
Fila: Implementada usando uma lista duplamente vinculada. A fila armazenará os quadros de página em ordem de uso, com os mais recentes próximos ao início e os menos usados próximos ao final. Hash: Usaremos um hash com o número da página como chave e o endere?o do nó correspondente na fila como valor.

已翻译

赞
Thiago Goes

Engenheiro Metalurgista | Master Black Belt | Gestor Ambiental | Gestor de Dados | Técnico em Minera??o | Técnico em Seguran?a do Trabalho
举报内容
A implementa??o do LRU com uma lista vinculada em Python envolve a cria??o de uma classe LRUCache que usa um dicionário para mapear páginas para nós da lista. Ao acessar uma página, o algoritmo verifica se ela já está na lista e a move para o início. Se n?o estiver na lista, a página é adicionada ao início e a última é removida se a capacidade for excedida.

已翻译

赞

4 What is the complexity of LRU with a linked list?

The complexity of the LRU algorithm with a linked list depends on the operations performed on the data structures. The hash map allows for constant time lookup of a page, while the doubly linked list allows for constant time insertion and deletion of a node. Therefore, the overall complexity of the LRU algorithm with a linked list is O(1) for each page request.

添加您的观点

Thiago Goes

Engenheiro Metalurgista | Master Black Belt | Gestor Ambiental | Gestor de Dados | Técnico em Minera??o | Técnico em Seguran?a do Trabalho
举报内容
A complexidade do algoritmo LRU com uma lista vinculada é geralmente eficiente, com opera??es de acesso, adi??o e remo??o de páginas realizadas em tempo constante O(1). Essa eficiência é devida à natureza das opera??es em listas vinculadas, tornando o LRU uma escolha prática para gerenciamento de memória.

已翻译

赞

5 What are the advantages and disadvantages of LRU with a linked list?

The advantages of the LRU algorithm with a linked list are that it is simple to implement, it has a low complexity, and it adapts well to the changing patterns of page accesses. The disadvantages of the LRU algorithm with a linked list are that it requires extra space for the hash map and the linked list, and it may not be optimal for some workloads that have a high degree of locality or cyclicality. For example, if a process accesses a set of pages repeatedly in a loop, the LRU algorithm will swap out the pages that are not in the loop, even though they may be used again soon.

添加您的观点

Thiago Goes

Engenheiro Metalurgista | Master Black Belt | Gestor Ambiental | Gestor de Dados | Técnico em Minera??o | Técnico em Seguran?a do Trabalho
举报内容
Vantagens da LRU com Lista Vinculada: Eficiência de Tempo Constante (O(1)): Opera??es principais s?o rápidas e têm complexidade constante. Simplicidade de Implementa??o: Implementa??o é direta e fácil de compreender. Desvantagens da LRU com Lista Vinculada: Espa?o Adicional: A lista vinculada requer espa?o adicional para armazenar os nós, o que pode ser uma desvantagem em ambientes com restri??es de memória. Complexidade de Código: Implementa??es precisam lidar com a manipula??o de ponteiros e podem ter código mais extenso em compara??o com outras abordagens. Acesso Aleatório Ineficiente: A busca por uma página específica na lista pode ser ineficiente em compara??o com estruturas de dados mais avan?adas, como hash tables.

已翻译

赞

6 How to improve LRU with a linked list?

One way to improve the LRU algorithm with a linked list is to use a variation called the second chance algorithm, which gives each page a second chance before swapping it out. The second chance algorithm uses a bit flag for each page, which is set to 1 when the page is accessed and cleared to 0 when the page is swapped out. When a page fault occurs, the algorithm scans the linked list from the tail to the head, looking for a page with a 0 flag. If it finds one, it swaps it out. If it does not, it wraps around to the tail again and clears the flags of all the pages, then repeats the scan. This way, the algorithm favors the pages that have been accessed recently, but also gives a chance to the pages that have been accessed less frequently.

添加您的观点

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

添加您的观点

Henry Korir

"IT Systems Engineer | Network Security & Cloud Solutions Expert | Advancing Digital Education"
举报内容
To implement LRU for page replacement you need to keep track of the order in which pages are accessed. This can be done using a data structure called a page table. Each entry in the page table contains the page number and a timestamp indicating when the page was last accessed. When a page needs to be replaced, the algorithm selects the page with the oldest timestamp, as it is the least recently used. This can be done by iterating through the page table and finding the entry with the smallest timestamp. To update the timestamp when a page is accessed, you need to modify the page table. This can be done by either updating the timestamp directly or by removing the page from the table and reinserting it at the front with a new timestamp.

已翻译

赞
Daniel Lim-Apo

Computer Science and Data Science University Graduation and Post Graduation Professor + Full Stack Developer
举报内容
We have the use of LRU useful to work with cache in games and applications written in javascript. The Least Recently Used (LRU) cache is a useful data structure for managing memory in games and applications where caching is critical to performance. The LRU cache helps manage memory efficiently by discarding the least recently used items when the cache reaches its maximum capacity.

已翻译

赞

Operating Systems

+ 关注

给文章评分

我们借助人工智能创建了此文章。您认为这篇文章怎么样？

很棒不太好

举报此文章

查看全部

How do you implement the LRU algorithm for page replacement?

1

2

3

4

5

6

7

1 What is LRU?

2 How to track page accesses?

3 How to implement LRU with a linked list?

4 What is the complexity of LRU with a linked list?

5 What are the advantages and disadvantages of LRU with a linked list?

6 How to improve LRU with a linked list?

7 Here’s what else to consider

Operating Systems

给文章评分

感谢您的反馈

更多Operating Systems相关文章

更多相关阅读内容

How do you implement the LRU algorithm for page replacement?

1

2

3

4

5

6

7

1 What is LRU?

2 How to track page accesses?

3 How to implement LRU with a linked list?

4 What is the complexity of LRU with a linked list?

5 What are the advantages and disadvantages of LRU with a linked list?

6 How to improve LRU with a linked list?

7 Here’s what else to consider

Operating Systems

给文章评分

感谢您的反馈

查看其他技能