Lru implementation details, Operating System

Assignment Help:

Now, let us discuss two related algorithms for deciding which pages to evict. The clock algorithm is one of the most popular choices. It works by keeping frames in a circular structure. (Note that this circle may be very large: a 32-bit machine with 4k pages can have up to 220  1 million frames.) When a page fault occurs, it checks the reference bit of the next frame. If that bit is zero, it evicts that page and sets its bit to 1; if the reference bit is 1, the algorithm sets the bit to 0 and advances the pointer to next frame. 

An implementation which is often used in real operating systems is a segmented queue. This type of algorithm divides all existing pages into two sets of pages. The most-active one-third of all pages use a clock algorithm. After that, pages that are evicted out of the clock are moved to a "uncommon" linked list, in which we use exact LRU. This way, we approximate LRU for the frequently-referenced pages (1/3 of the page frames - fast clock algorithm), and at the same time use exact LRU on the infrequently accessed pages (2/3 of all page frames). Since the pages in the uncommon list are not accessed very frequently, it is okay if their accesses are a little slower due to some pointer manipulation.


Related Discussions:- Lru implementation details

Define lru page replacement algorithm, Define LRU Page Replacement Algorith...

Define LRU Page Replacement Algorithm LRU policy: LRU expands to least currently use. This policy suggests which we re- move a page whose last usage is farthest from current ti

Explain external fragmentation?, Explain external fragmentation? Extern...

Explain external fragmentation? External fragmentation is the process where the free space and the space still available for use, in a piece of storage become separated into ma

Define spooling, Define spooling. A spool is a buffer that holds output...

Define spooling. A spool is a buffer that holds output for a device, like printer, that cannot accept interleaved data streams. When a request finishes printing, the spooling s

What are race conditions?, What are race conditions? Race conditions ar...

What are race conditions? Race conditions are problems that take place due to the sharing of the same file by several processes. In such a case none of the processes is able to

How many disk operations are needed to fetch the i-node, How many disk oper...

How many disk operations are needed to fetch the i-node for the file /usr/ast/courses/os/handout.t? Assume that the i-node for the root directory is in memory, but nothing else alo

What are the advantages of using unequal- size partitions, In fixed portion...

In fixed portioning scheme, what are the advantages of using unequal- size partitions? With unequal-size partitions there are two probable ways to assign process to partitions.

Compression regarding the file system in windows 2000, Write short note on ...

Write short note on compression regarding the file system in Windows 2000. NTFS is able to perform data compression on individual files or on all data files in a directory. To

Requirements to satisfied by the critical section problem, What are the req...

What are the requirements to be satisfied by the critical section problem? Following are the necessities to be satisfied by the critical section problem: a)      Mutual exc

Explain important fuction of virtual file system, Virtual File System serve...

Virtual File System serves two important functions. 1. It divides file-system-generic operations from their execution by defining a clean VFS interface. 2. The VFS is based

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd