Os Memory Management Questions Medium
A page replacement algorithm is used in operating systems to manage the allocation and deallocation of memory pages. It is responsible for selecting which pages to evict from the main memory when a new page needs to be brought in.
The working of a page replacement algorithm typically involves the following steps:
1. Page Fault: When a process requests a page that is not currently present in the main memory, a page fault occurs. This triggers the page replacement algorithm to select a page to be replaced.
2. Page Selection: The page replacement algorithm selects a victim page from the main memory to be replaced. The selection is based on certain criteria, such as the page's access history, frequency of use, or time since last access. Different algorithms use different criteria to make this decision.
3. Page Eviction: The selected victim page is evicted from the main memory and moved to secondary storage, such as the hard disk. If the page has been modified (dirty), it needs to be written back to the disk before eviction.
4. Page Loading: The requested page is then loaded from secondary storage into the newly freed space in the main memory. This allows the process to continue its execution without any interruptions.
5. Update Page Tables: The page tables are updated to reflect the new location of the page in the main memory. This ensures that the process can access the page correctly.
6. Continue Execution: The process resumes its execution with the newly loaded page in the main memory.
Different page replacement algorithms have different characteristics and trade-offs. Some popular algorithms include the Optimal algorithm, Least Recently Used (LRU), First-In-First-Out (FIFO), and Clock algorithm. Each algorithm aims to optimize the memory usage and minimize the number of page faults, but they may have different levels of efficiency and complexity.