This algorithm helps to decide which pages must be swapped out from the main memory in order to create a room for the incoming page.
A-frame can be freed by writing its content to swap space and then change the page table in order to indicate that the page is no longer in the memory.įirst of all, find the location of the desired page on the disk.Ī) If there is a free frame, then use it.ī) If there is no free frame then make use of the page-replacement algorithm in order to select the victim frame.Ĭ) Then after that write the victim frame to the disk and then make the changes in the page table and frame table accordingly.Īfter that read the desired page into the newly freed frame and then change the page and frame tables.įigure: Page Replacement Page Replacement Algorithms in OS If there is no free frame, then we will find the one that is not currently being used and then free it. Page Replacement technique uses the following approach. Page Fault – It is basically a memory error, and it occurs when the current programs attempt to access the memory page for mapping into virtual address space, but it is unable to load into the physical memory then this is referred to as Page fault. The main objective of all the Page replacement policies is to decrease the maximum number of page faults. In Virtual Memory Management, Page Replacement Algorithms play an important role. This technique provides complete separation between logical memory and physical memory. To reduce the overhead of page replacement a modify bit (dirty bit) is used in order to indicate whether each page is modified. Page replacement prevents the over-allocation of the memory by modifying the page-fault service routine. And all these require double the disk access time. The Operating system must then write the victim frame to the disk then read the desired page into the frame and then update the page tables. The operating system must use any page replacement algorithm in order to select the victim frame. In this case, if a process requests a new page and supposes there are no free frames, then the Operating system needs to decide which page to replace. This technique is called Page replacement and is most commonly used. Or, find some pages that are not being used right now, move them to the disk to get free frames. Or, remove some other process completely from the memory to free frames. Put the process in the wait queue, until any other process finishes its execution thereby freeing frames. Following steps can be taken to deal with this problem : but what happens when a process requests for more pages and no free memory is available to bring them in. This allows us to get more processes into memory at the same time.
In this tutorial, we will be covering the concept of Page replacement and its algorithms in the Operating system.Īs studied in Demand Paging, only certain pages of a process are loaded initially into the memory. Longest Remaining Time First Scheduling.
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