Evicting pages from physical memory, Operating System

Assignment Help:

When do we write a page from physical memory back to the disk?

In general, caches have two broad types of writing policies. One approach is a write-through cache. In this case, when a value in the cache is written, it is immediately written to the backing store as well (in this case, the disk). The cache and backing store are always synchronized in this case, but this can be very slow. The other main approach is a write-back cache. In this case, the backing store and the cache are sometimes out of sync, but this approach is much faster. This is what is used with paging, for obvious speed reasons.

When a page is loaded from the disk to physical memory, it is initially clean, i.e. the copy in physical memory matches the copy on disk. If the copy in memory is ever changed, then its page-table entry is marked dirty, and it will need to be written back to the disk later. When physical memory ?lls up, and a non-resident page is requested, then the OS needs to select a page to evict, to make room for the new page. The evicted page is called the victim, and is saved to the so-called "swap" space.

The swap space is a separate region of the disk from the ?le system, and the size of the swap space limits the total virtual address space of all programs put together (though in practice, there is a lot of memory shared between processes, for instance shared libraries). There are a variety different strategies for choosing which page to evict, with tradeoffs for each strategy. These strategies will be discussed later. One thing to note is that evicting a clean page is fast, since it doesn't need to be written back to the disk. A second note is that to speed up the process of evicting pages, the OS can write dirty pages back to disk as a background task. In this way, more pages will be clean and can therefore be evicted a lot more quickly, when it is time to do so.


Related Discussions:- Evicting pages from physical memory

Financial objective of corporation, The primary financial objective of corp...

The primary financial objective of corporation is usually taken to be the maximization of shareholder wealth. Discuss:- i. Ways in which the shareholder of a company can encour

When page fault frequency in an operating system is reduced, When the Page ...

When the Page fault frequency in an operating system is reduced Locality of reference is appropriate to the process

Mechanism by which one segment belong to two address spaces, Q. Explain a m...

Q. Explain a mechanism by which one segment could belong to the address space of two different processes. Answer: Because segment tables are a collection of base-limit register

List sample file types, List sample file types, based on use, on the VAX un...

List sample file types, based on use, on the VAX under VMS.  source programs (.BAS, .FOR, .COB, .PLI, .PAS, .MAR)  data files (.DAT)  text files (.TXT)  command proced

Virtual memory, How a virtual memory can be implemented? What are the benef...

How a virtual memory can be implemented? What are the benefits of using virtual memory?

Explain about time sharing systems, Q. Explain about Time Sharing Systems? ...

Q. Explain about Time Sharing Systems? Time Sharing Systems Multi-programmed batched systems provide an environment where various system resources (for illustration CP

Identify the binding and non-binding constraints, Crumbles Bakery needs to ...

Crumbles Bakery needs to decide how many and what types of cupcakes to make today. Currently, they make two types of cupcakes: chocolate cupcakes and carrot cake cupcakes. Chocolat

Problem of unbalanced loads, Present your own fully documented and tested p...

Present your own fully documented and tested programming example illustrating the problem of unbalanced loads. Describe the use of OpenMP's scheduler as a means of mitigating this

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