Page Replacement Algorithm

✅ Page Replacement Algorithm

• in OS that uses paging for memory management
• which page should be replaced when a new page comes in
• used 1️⃣ when page fault occurs and 2️⃣ there is no free page in memory

💡 Paging https://soheeparklee.github.io/posts/OS-12paging/

✔️ Page Replacement Algorithm

• FIFO
• Optimal Page Replacement
• Least Recently Used
• Most Recently Used

✅ Page fault

• program accesses memory page
• memory page that is mapped into virtual address space
• but not loaded on physical memory

💡 Virtual Memory https://soheeparklee.github.io/posts/OS-virtualmemory/

• if page fault occurs,
• OS need to replace page with newly added page

☑️ FIFO

First in first out

• oldest(first) in memory to SWAP
• keep track of pages in memory in queue

☑️ Optimal Place Replacement

• which page would not be used for the longest duration in the future?
• check future access pattern
• select page based on pattern
• and send to SWAP
• 👎🏻 not possible in practice as OS cannot know future requests

☑️ LRU

Least Recently Used

• page with most time that is not used

☑️ MRU

Most Recently Used

• page that has been used recently

☑️ LFU

Least Frequently Used

• least use frequency

☑️ NUR

Not Recently Used page replacement

• page that has not been referenced in atleast one clock tick