Multi-level page tables, Operating System

Assignment Help:

Multi-level page tables are tree-like structures to hold page tables. As an example, consider a two- level page table, again on a 32-bit architecture with 212 = 4 kbyte pages. Now, we can divide the virtual address into three parts: say 10 bits for the level-0 index, 10 bits for the level-1 index, and again 12 bits for the offset within a page.

The entries of the level-0 page table are pointers to a level-1 page table, and the entries of the level-1 page table are PTEs as described above in the single-level page table section. Note that on a 32-bit architecture, pointers are 4 bytes (32 bits), and PTEs are typically 4 bytes.

So, if we have one valid page in our process, now our two-level page table only consumes (210

level-0 entries)(22
bytes/entry)+1(210
level-1 entries)(22
bytes/entry) = 2212
bytes = 8 kbytes:

For processes with sparse virtual memory maps, this is clearly a huge savings, made possible by the additional layer of indirection.

Note that for a process which uses its full memory map, that this two-level page table would use slightly more memory than the single-level page table (4k+4M versus 4M). The worst-case memory usage, in terms of ef?ciency, is when all 210 level-1 page tables are required, but each one only has a single valid entry.

In practice, most page tables are 3-level or 4-level tables. The size of the indices for the different levels are optimized empirically by the hardware designers, then these sizes are permanently set in hardware for a given architecture.


Related Discussions:- Multi-level page tables

What are the issues in designing a network, Normal 0 false fa...

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4

What are the characteristics of srs, What are the characteristics of SRS? ...

What are the characteristics of SRS? i. Correct - The SRS should be made up to date when appropriate requirements are identified. ii. Unambiguous - When the requirements are

Difference between preemptive and nonpreemptive scheduling, Define the diff...

Define the difference between preemptive and nonpreemptive scheduling. State why strict nonpreemptive scheduling is unlikely to be used in a computer center. Preemptive schedul

Data transfer between two processes, Q. Data transfer between two processes...

Q. Data transfer between two processes? Communication: Data transfer between two processes is essential for some time. Both processes are on the one computer or on different

Activities of an operating system, Q. What are the five main activities of ...

Q. What are the five main activities of an operating system in regard to process management? Answer: a. The creation as well as deletion of both user and system processes

Describe the differences among short-term and medium-term, Describe the dif...

Describe the differences among short-term, medium-term, and long-term scheduling.   Short-term (CPU scheduler)-selects from jobs in memory those jobs that are ready to execu

What is a general graph, What is a general graph? A tree structure wher...

What is a general graph? A tree structure where links can go from one branch to a node earlier in the similar branch or other branch, allowing cycles.

Explain what is file structure, Problem 1. List out the conditions that...

Problem 1. List out the conditions that result in Deadlock situations. Illustrate deadlock situation with a simple graphical notation Listing conditions for deadlock occu

Name two differences between logical and physical addresses, Q. Name two di...

Q. Name two differences between logical and physical addresses? Answer: A logical address doesn't refer to an actual existing address rather it refers to an abstract address in

Explain how indefinite blocking or starvation occur, explain how indefinit...

explain how indefinite blocking or starvation occurs..

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