Sharing memory, Operating System

Assignment Help:

As we have discussed, page tables map virtual page addresses to physical page addresses. One of the advantages of using virtual addresses is that we can achieve complete separation between processes, in terms of address spaces. One drawback to this is that it is convenient to be able to share some things, for example library code which would otherwise be replicated wastefully by many different programs. We don't want to have to load exactly the same library code into every process' address space; we'd prefer to map the library code to its own pages, and let all processes share those pages. This will usually reduce the memory requirements for the system. In order to do this, we need to do some common tricks with page tables.

The ?rst important memory-sharing concept is known as Copy-On-Write, or COW. COW shares pages by default, whenever sharing is still possible. Whenever a new process is created, for example by fork(), we "clone" an old process by making a copy of its page tables and marking all referenced pages as read-only.

Then whenever either of the processes (the original one, or the clone) tries to write to one of the pages, the two processes will differ, and sharing is no longer possible. The OS allocates a new page and changes the mapping in one of the page tables. If neither of the processes ever tries to modify a memory location, however, the processes will share the same (read-only) pages forever! COWtries to maximize the amount of sharing at all times.


Related Discussions:- Sharing memory

Installation and Training Documentation, Ask question Project Details PROJE...

Ask question Project Details PROJECT OVERVIEW The ABC Hospital is upgrading their version of Windows. As part of the upgrade, 100 new computers will be purchased. Your task is to

What is the use of FIFOs in client-server applications, What is the use of ...

What is the use of FIFOs in client-server applications

Linear Programing, . A paper mill produces two grades of paper viz., X and ...

. A paper mill produces two grades of paper viz., X and Y. Because of raw material restrictions, it cannot produce more than 400 tons of grade X paper and 300 tons of grade Y paper

What is banker''s algorithm, What is banker's algorithm? Banker's algor...

What is banker's algorithm? Banker's algorithm is a deadlock avoidance algorithm that is applicable to a resource-allocation system with multiple examples of each resource type

What are the three main activities of an operating system, What are the thr...

What are the three main activities of an operating system in regard to memory management? Keep track of which parts of memory are now being used and by whom. Decide which pr

#title.paging, explain hierarchical,hashed and inverted paging

explain hierarchical,hashed and inverted paging

Determine the task of the pass ii in a two-pass assembler, Determine the ta...

Determine the task of the Pass II In a two-pass assembler Synthesize the target program is the task of the Pass II

Explain how protection is provided for the hardware resource, Explain how p...

Explain how protection is provided for the hardware resources by the operating system. Dual mode operation Sharing system resources needs operating system to make sure

VB. Net & XML, Write a XML with database with book details (BOOK ID, Title,...

Write a XML with database with book details (BOOK ID, Title, Author, subject, publisher year, language, vendor, and price)

Implement a network-transparent system, Q. What are two dreadful problems t...

Q. What are two dreadful problems that designers should solve to implement a network-transparent system? Answer: One such issue is making all the processors as well as storag

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