Mastering Page Replacement Algorithms in Operating Systems: A Quick, Deep Dive
Mastering Page Replacement Algorithms in Operating Systems: A Quick, Deep Dive
Blog Article
When your computer runs more programs than its physical memory can hold, the operating system uses page replacement algorithms to decide which memory pages to swap out and which to keep. This decision is crucial for performance and efficiency
Why do we need them?
Whenever a program requests a memory page not currently in RAM (a page fault), the OS must make room by removing an existing page.
Popular Algorithms:
FIFO (First-In, First-Out):
The oldest page in memory is replaced first. It’s simple but can perform poorly, sometimes causing more faults as memory increases—a phenomenon called Belady’s anomaly.
Optimal:
Replaces the page that won’t be used for the longest time in the future. It’s unbeatable in theory but impossible to implement, since the OS can’t predict the future.
LRU (Least Recently Used):
Removes the page that hasn’t been used for the longest time, assuming recently used pages will be needed again soon. LRU is practical and effective but needs extra bookkeeping.
Random:
Picks any page at random to replace. It’s easy to implement but unpredictable in performance.
Each algorithm balances simplicity, efficiency, and practicality. In real-world systems, LRU and its variants are often favored for their balance of performance and feasibility. Understanding these algorithms is key to mastering how modern operating systems manage memory under pressure
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