Os Memory Management Questions Medium
The LRU (Least Recently Used) page replacement algorithm is a memory management technique used by operating systems to decide which pages to evict from the main memory when it becomes full and a new page needs to be brought in. The basic idea behind LRU is to replace the page that has not been accessed for the longest period of time.
The working of the LRU algorithm can be explained as follows:
1. Each page in the main memory is associated with a timestamp or a counter that keeps track of the last time the page was accessed.
2. When a page needs to be replaced, the operating system examines the timestamps or counters of all the pages in the memory to determine which page has the oldest timestamp or the lowest counter value. This page is considered the least recently used.
3. The page with the oldest timestamp or the lowest counter value is then selected for replacement and is evicted from the main memory.
4. The new page that needs to be brought into the memory is then loaded into the vacant space left by the evicted page.
5. The timestamp or counter of the newly loaded page is updated to reflect the current time or counter value.
By using the LRU algorithm, the operating system aims to minimize the number of page faults, which occur when a requested page is not found in the main memory. The assumption is that the pages that have been accessed recently are more likely to be accessed again in the near future, while the pages that have not been accessed for a long time are less likely to be accessed again.
However, implementing the LRU algorithm can be computationally expensive, as it requires keeping track of the access history of each page. Various data structures, such as linked lists or priority queues, can be used to efficiently maintain the order of the pages based on their access timestamps or counters.
Overall, the LRU page replacement algorithm is a widely used and effective technique for managing memory in operating systems, as it prioritizes the retention of frequently accessed pages in the main memory.