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

What is belady anomaly, What is Belady's anomaly When plotting on a g...

What is Belady's anomaly When plotting on a graph the page faults versus the number of available frames. We notice that the number of faults for four frames is greater than th

Determine the syntax of the assembler directive equ, Determine the syntax o...

Determine the syntax of the assembler directive EQU The following is syntax of the assembler directive EQU: EQU

Relationship among a(x, Q. The RC 4000 system as well as other systems hav...

Q. The RC 4000 system as well as other systems have defined a tree of processes (called a process tree) such that all the descendants of a process are given resources (objects) as

Explain the fork function, Explain the Fork Function Fork function caus...

Explain the Fork Function Fork function causes a new process to be created. The calling progress is duplicated as an exact copy (called the child process) that differs only in

Explain benefits of time-sharing system, Under what circumstances would a ...

Under what circumstances would a user be better off using a time-sharing system, rather than a personal computer or single-user workstation? When there are some other users, th

Aggregate planning, Prepare a report that motivates alternatives reactive s...

Prepare a report that motivates alternatives reactive strategies that can be used by wind Mud clothing factory

Linear programming problem, A paper mill produces two grades of paper viz.,...

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 ton

Management Information Systems, Select any business process within this fir...

Select any business process within this firm, describe it as a set of steps then fill the following table (flow, information, sender and receivern #Minimum 100 words accepted#

What are overlays, What are overlays? To enable a process to be larger ...

What are overlays? To enable a process to be larger than the amount of memory allocated to it, overlays are used. The idea of overlays is to keep in memory only those instructi

List the various file attributes, List the various file attributes. A f...

List the various file attributes. A file has particular other attributes, which vary from one operating system to another, but typically having of these:  Name, identifier, typ

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