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

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

Semaphores, how do semaphores help us in eliminating deadlock conditions?

how do semaphores help us in eliminating deadlock conditions?

Explain the architecting for processes, Explain the Architecting For Proces...

Explain the Architecting For Processes Processes are very important to the server application developer, as they may be used to increase responsiveness, deduction time, and tur

What is an operating system, What is an operating system? An operating ...

What is an operating system? An operating system is a program that manages the computer hardware. It acts as an intermediate among users of a computer and the computer hardware

Characteristics of suspend process, Characteristics of suspend process ...

Characteristics of suspend process Suspended process isn't immediately available for execution. The process may or may not be waiting on an event. For preventing t

Linux operation system, wat are the commands used for creating the file hie...

wat are the commands used for creating the file hierarchy

Semispace, Semispace works by maintaining two disjoint areas from which mem...

Semispace works by maintaining two disjoint areas from which memory can be allocated. These areas are called the from-space and the to-space. At ?rst, the algorithm allocates memor

What is the design issues involved in segmentation?, SEGMENTATION HARDWARE ...

SEGMENTATION HARDWARE An execution to map two-dimensional user-defined addresses into one-dimensional physical addresses. This mapping is affected by means of segment table. Ev

Naming scheme for servers in an enterprise, Problem: Within a corporate...

Problem: Within a corporate environment, there are usually many servers located across various departments. Naming of servers is often a tedious task. In many circumstances, w

Explain concept of synchronization, Synchronization In communication am...

Synchronization In communication among processes messages passed may be blocking or nonblocking - also called as synchronous and asynchronous. Blocking send : The sending pr

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