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

Solve a generalized dining philosopher problem, In this project, you will i...

In this project, you will implement the Chandy and Misra's (CM) algorithm using POSIX Threads (Pthreads).   The algorithm  is a distributed algorithm to solve a generalized dining

What are turnaround time and response time, What are turnaround time and re...

What are turnaround time and response time? Turnaround time is the interval among the submission of a job and its completion. Response time is the interval among submission

Linux kernel components, Example 1.  The diagram illustrating the data stru...

Example 1.  The diagram illustrating the data structures of in-memory VFS objects and on-disk objects and their relationships on slide 24 of the lecture notes OSD.4. This diagram i

What are the advantages of indexed allocation, What are the advantages of I...

What are the advantages of Indexed allocation? The benefits are a. No external-fragmentation problem b. Solves the size-declaration problems. c. Supports direct access

Cpu, what is cpu

what is cpu

Write in brief on unix file structure, Write in brief on UNIX file structur...

Write in brief on UNIX file structure. UNIX considers every file to be a sequence of 8-bit bytes no interpretation of these bits is made by the operating system. This system pr

Invalid page fault, Invalid page fault :If a page fault happens for a ref...

Invalid page fault :If a page fault happens for a reference to an address that's not part of the virtual address space, so that there could not be a page in memory corresponding

Explain a boot control block, Explain a boot control block A boot contr...

Explain a boot control block A boot control block can have the information required by the system to boot an operating from that partition. If the disk does not have an operati

Explain the benefits of thread over process?, BENEFITS OF THREADS OVER PROC...

BENEFITS OF THREADS OVER PROCESS If implemented correctly after those threads have some advantages of (multi) processes, they take: 1. Less time to create a new thread tha

Explain single partition allocation., Operating Systems 1. Explain sing...

Operating Systems 1. Explain single Partition Allocation and Multiple Partition Allocation. 2. What do you mean by PCB? What useful information is available in PCB? 3. De

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