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

Scheduler that select process from secondary storage device, A scheduler th...

A scheduler that selects processes from secondary storage device is known as                    Medium term scheduler is a scheduler that selects processes from secondary stor

Action taken by the operating system when a page fault occur, Q. Under what...

Q. Under what conditions do page faults occur? Explain the actions taken by the operating system when a page fault occurs. Answer: A page fault take places when an access to

Interval between time of submission and completion of job, Interval among t...

Interval among the time of submission and completion of the job is known as                    Interval among the time of submission and completion of the job is known as Turn

What is preallocation, What is preallocation? Why do it? Allocating spa...

What is preallocation? Why do it? Allocating space for a file before making the file to allow for expansion. This reserves space for a certain file so that other files can't gr

integrator circuit, Referring to Figure below, discuss how you would alter...

Referring to Figure below, discuss how you would alter the circuit to obtain: 1. a straightforward amplifier with gain 1, 2. a straightforward amplifier with gain 10, 3. a

Define rotational latency and disk bandwidth, Define rotational latency and...

Define rotational latency and disk bandwidth. Rotational latency is the additional time waiting for the disk to rotate the wanted sector to the disk head. The disk bandwidth is

Memory hierarchy, Difference between cache and associate memory

Difference between cache and associate memory

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

Fcfs scheduling algorithm, Q. Presume that the following processes arrive f...

Q. Presume that the following processes arrive for execution at the times indicated. Every process will run the listed amount of time. In responding the questions use non pre-empti

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