Question: Discuss the effect of page size on the performance of operating system

Mumbai University > COMPS > Sem 5 > Operating System

Marks: 2 M & 5 M

Year: May 2015, Dec 2016 & May 2017

modified 10 months ago by gravatar for Abhishek Tiwari Abhishek Tiwari ♦♦ 50 written 3.5 years ago by gravatar for 0309rishika 0309rishika10

Effect of page size on performance

  • The number of frames is equal to the size of memory divided by the page-size. So and increase in page size means a decrease in the number of available frames.
  • Having a fewer frames will increase the number of page faults because of the lower freedom in replacement choice.
  • Large pages would also waste space by Internal Fragmentation.
  • On the other hand, a larger page-size would draw in more memory per fault; so the number of fault may decrease if there is limited contention.
  • Larger pages also reduce the number of TLB misses.
written 3.5 years ago by gravatar for 0309rishika 0309rishika10

Thanx a Lot!! It was very Helpful

written 3.3 years ago by gravatar for 0309rishika 0309rishika10

An important hardware design decision is the size of page to be used. There are several factors to consider.

Internal fragmentation:

  • Clearly, the smaller the page size, the lesser is the amount of internal fragmentation. To optimize the use of main memory, we would like to reduce internal fragmentation.
  • On the other hand, smaller the page, the greater is the number of pages required per process which could mean that some portion of page tables of active processes must be in virtual memory, not in main memory. This eventually leads to double page fault for a single reference of memory.

Rate at which page fault occurs:

  • If the page size is very small , then ordinarily a large number of pages will be available in main memory for process,which after some time will contain portions of process near recent references leading to low page fault rate.
  • As the size of page is increased, each individual page will contain locations further and further from any particular recent reference. Thus, the effect of the principle of locality is weakened and the page fault rate begins to rise.
  • Eventually, however the page fault rate will begin to fall as the size of page approaches the size of the entire process.

Typical paging behavior of  Program

Size of physical main memory and program size:

  • For a given size of TLB, as the memory size of processes grows and s locality decreases, the hit ratio on TLB declines. Under these circumstances, the TLB can become a performance bottleneck.
modified 2.1 years ago by gravatar for Kamal Keswani Kamal Keswani0 written 2.1 years ago by gravatar for 0309rishika 0309rishika10
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