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

Question 3:, Question 3: (a) Fincorp Ltd is an insurance company wishing t...

Question 3: (a) Fincorp Ltd is an insurance company wishing to change over to a better business system using an improved version of a financial information system (FIS). The direc

Programable clock modes in computer systems, Ask question #Minimuexplain th...

Ask question #Minimuexplain the programable clock modes in a computer system m 100 words accepted#

System protection, what is the need-to-know principle? why is it important ...

what is the need-to-know principle? why is it important for a protection system to adhere to this principle?

Explain about disk scheduling with neat diagram, Explain about disk schedul...

Explain about disk scheduling with neat diagram? FCFS Scheduling SCAN scheduling C-SCAN scheduling SSTF scheduling LOOK Scheduling

Mark-sweep, The objects that a program can access directly are those object...

The objects that a program can access directly are those objects which are referenced by local vari-ables on the processor stack, or by any global/static variables that refer to ob

Explain deadlock prevention, Deadlock Prevention Prevention is the name...

Deadlock Prevention Prevention is the name given to method that guarantee that deadlocks can never happen for the reason that the way the system is structured. Since 4 conditio

What is graceful degradation, What is graceful degradation? In multipro...

What is graceful degradation? In multiprocessor systems, failure of single processor will not halt the system, but only slow it down by sharing the work of failure system by ot

Write a brief note on demand paging, Write a brief note on demand paging. ...

Write a brief note on demand paging. A demand paging is alike to a paging system with swapping. The Processes reside on the secondary memory while we want to implement a proces

Write a short note about process, Write a short note about process. Unc...

Write a short note about process. Unceremoniously, a process is a program in implementation. A process is too much than the program code, which is occasionally known as the tex

Drawbacks of least-recently used algorithm, The question of fairness, regar...

The question of fairness, regarding page eviction, is a hard one. How do we decide what is fair? Many operating systems use global LRU, where pages from all processes are managed t

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