Skip to main content

Performance Of Demand Paging In O/S

 As we Know  when we load the entire program in physical memory at program execution time, Known as paging. And when we load pages of program only as they are neede, known as demand paging and commonly used in virtual memory system. With demand paging, virtual memory pages are loaded only when they are demanded during program execution. Pages that that are never accessed are thus never loaded into physical memory (RAM).
  
So, demand paging can significantly affect the performance of a computer system. To see how demand paging affect the performance of computer system, let's compute the 'effective access time' for a demand-paged memory. For most computer systems, the memory-access time is denoted by ma, ranged from 10 to 200 nanoseconds. As long as we have no page faults, the effective access time is equal to the memory access time. But if a page fault occurs, we must first read the relevant page from disk and then access the desired word.

To complete the effective access time, we must know how much time needed to service a page fault. A page fault cause following sequence to occur :-
  • Trap to the operating system.
  • Save the user register and process state.
  • Determine that the interrupt was a page fault.
  • Determine the location of the page on the disk.
  • While waiting, allocate the CPU to some other user.
  • Recieve an interrupt from the disk I/O subsystem.
  • Save the registers and process state for the other user.
  • Determine that the interrupt was from the disk.
  • Correct the page table to show that the desired page is now in memory.
  • Wait for the CPU to be allocated to this process again.
  • Restore the user register, process state, and new pagetable, and then resume the interrupted instruction.
Not all of these steps are necessary in every case. In any case, we are facing with three major compounds of the page-fault service time :-
  1. Service the page-fault interrupt.
  2. Read in the page.
  3. Restart the process.
The first and third tasks can be, with careful coding, to several hundred instructions. These tasks may take from 1 to 100 microsecond.

An addiotional maspect of demand paging is the handling and ovarall use vof swap space. Disk I/O swap space is generally faster than thjat to the file system.
some systems attempt to limit the amount of swap space used through demand paging of binary files.

Share, Follow and please comment if you find anything incorrect or to share more information about the topic discussed above.
Labels:

Comments

Post a Comment

Please comment.

Popular posts from this blog

Process Scheduling And Types of Process Schedular :-

        ⇰ PROCESS SCHEDULING Process Scheduling  is a task  of Operating System that schedules processes of different states like new, ready, waiting, terminated  and running.This scheduling helps in allocation of CPU time for each process, and Operating System allocates the CPU time for each procss. And the process scheduling plays important role to keep the CPU busy all the time.  ⏩   Followings are some objectives of Process Scheduling :-  i > To increase the amount of users within acceptable response times.  ii > To maintain the balance between response and utilization of system. iii > To decrease the enforce priorities and  give reference to the processes holding the key resources.      ⇰  PROCESS SCHEDULAR A scheduler carries out the pro cess scheduling work. Schedulers are often implemented so they keep all computer resources busy and  allows multiple users to share system resources  to achieve  multiprogramming .  There are  mainy three types of pro
8 comments
Read more

Tokens and its types in 'C'

   Tokens are the smallest individual unit of a program or in simple words it is a main part of C program.Tokens are the building blocks of any program. The smallest individual and basic unit of a C programming is called c tokens.      *    Normally there are six types of tokens in C:- i> Keywords:-          Keywords are special words that are used to give a special meaning to the program and can't be used as variable and constant.They are basically a sequence of characters that have fixed to mean. For example:-                 auto     double      long     break                 float    short        char     if                while    continue   int       void etc. All keywords must be written in lower case.It is 32 in number. ii> Identifiers:-         The identifiers are basically a token. It can be a variable's name or a label's name. So identifiers are actually a user defined data. But there are certain rules to frame an identifier. They are as follo
3 comments
Read more

Micromax 'The Indian Smart Phone Company'

Micromax  is an Indian  consumer electronics  company headquartered in  Gurgaon ,  Haryana . It was established as an  IT   Software  company operating in the  Embedded Devices   Domain . It later entered the  Mobile   Handset  business. Micromax was incorporated as Micromax Informatics Ltd. on 29 March 2000 by Zeeshan Ali Zaidi. It began selling mobile telephones in 2008,  focusing on  low pricing to compete with international brands. By 2010, Micromax was one of the largest domestic companies making handsets in the low-cost feature phone segment in India. As of Q3 2014, Micromax is the  Tenth Largest   Smart phone  vendor in the world. The company is facing stiff competition from Chinese companies that are penetrating the Indian market. The company also owns  YU Televentures , which sells its products under the brand name YU. The company has also introduced handsets with innovative features. For instance, Micromax's co-founder  Rahul Sharma  once saw a  public call
2 comments
Read more