CS5460: Operating Systems Lecture 16: Page Replacement (Ch. 9)

Save this PDF as:
 WORD  PNG  TXT  JPG

Size: px
Start display at page:

Download "CS5460: Operating Systems Lecture 16: Page Replacement (Ch. 9)"

Transcription

1 CS5460: Operating Systems Lecture 16: Page Replacement (Ch. 9)

2 Last Time: Demand Paging Key idea: RAM is used as a cache for disk Don t give a process a page of RAM until it is needed When running short on RAM, take pages away from processes This only works if accesses to memory pages have high temporal locality» Why don t we care about spatial locality? Three basic kinds of page table entries Valid mapping the OS is not involved translation performed entirely by the CPU Invalid mapping trap, then kernel does something special, such as kill the process Valid but not present trap and do demand paging Demand paging makes the exec() system call fast

3 Timeline of a Page Fault 1. Trap to operating system 2. Save state in PCB 3. Vector to page fault handler 4. If invalid, send SIGSEGV 5. If valid, find or create a free page a. Possibly involves disk write 6. Issue disk read for page a. Wait until request queued at disk controller b. Wait for seek/latency c. Wait for data transfer (DMA) d. Wait for completion interrupt 7. (Optional) Schedule another process while waiting 8. Take disk interrupt 9. Update page table 10. Add process to run queue 11. Wait for process to be scheduled next 12. Restore state from PCB 13. Return from OS 14. Re-execute faulting instruction

4 Effective Access Times What is average access latency? L1 cache: 2 cycles L2 cache: 10 cycles Main memory: 150 cycles Disk: 10 ms à 30,000,000 cycles on 3.0 GHz processor Assume access have following characteristics:» 98% handled by L1 cache» 1% handled by L2 cache» 0.99% handled by DRAM» 0.01% cause page fault Average access latency:» (0.98 * 2) + (0.01 * 10) + ( * 150) + ( * 30,000,000) = = about 3000 cycles / access Moral: Need LOW fault rates to sustain performance!

5 Issues in Demand Paging Page selection policy When do we load a page? Page replacement policy What page(s) do we swap to disk to make room for new pages? When do we swap pages out to disk? How do we handle thrashing?

6 Demand paging: Page Selection Policy Load page in response to access (page fault) Predominant selection policy Pre-paging (prefetching) Predict what pages will be accessed in near future Prefetch pages in advance of access Problems:» Hard to predict accurately (trace cache)» Mispredictions can cause useful pages to be replaced Overlays Application controls when pages loaded/replaced Only really relevant now for embedded/real-time systems

7 Optimal Page Replacement Policies Throw out page used farthest in the future Random Works surprisingly well FIFO (first in, first out) Throw out oldest pages LRU (least recently used) Throw out page not used in longest time NRU (not recently used) Approximation to LRU à do not throw out recently used pages How should we evaluate page replacement policies?

8 FIFO Page Replacement FIFO: replace oldest page (first loaded) Example: Memory system with three pages à all initially free Reference string: A B C A B D A D B C B Frame1 Frame2 Frame3 A B C A B D A D B C B A D C B A C B Result: 7 page faults

9 Optimal Page Replacement Optimal: replace page used farthest in the future Example: Memory system with three pages à all initially free Reference string: A B C A B D A D B C B Frame1 Frame2 Frame3 A B C A B D A D B C B A C B C D C Result: 5 page faults

10 LRU Page Replacement LRU: replace least recently used page Example: Memory system with three pages à all initially free Reference string: A B C A B D A D B C B Frame1 Frame2 Frame3 A B C A B D A D B C B A C B C D Result: 5 page faults

11 How would you implement Random FIFO Optimal LRU NRU Which ones are efficient?

12 NRU Page Replacement Observations LRU is pretty good approximation of OPT» Past performance is often reasonable predictor of future performance» Captures phase behavior in many (but not all) applications Implementing true LRU requires far too much overhead» Logically, need to update sort order on every memory access How can we approximate LRU efficiently? Exploit referenced bit in modern page tables Only replace pages that have not been recently referenced (NRU) Periodically clear referenced bits à enforces recently» Optionally: Maintain recent history of referenced bits per-page» Example: à denotes times page referenced last 8 sweeps

13 NRU Page Replacement This is a modified version of FIFO Checks if the page at the head of the FIFO queue has its referenced bit set Yes? Then clear the bit and put it at the back of the queue and look at the next page No? Then select this page Is this fast? What is the worst case? This is called the second chance algorithm

14 Clock Algorithm This is basically an optimized version of second chance Maintains next pointer Starts sweep there until done Persists across invocations While (need more pages) Check referenced bit If 0 à add to free pool If 1 à reset bit Between sweeps If a process accesses page, referenced bit gets set TLB helps here! Next Next Next Next Next Referenced Free! Free!

15 BSD Page Replacement (NRU) Goal: maintain pool of free pages at all times Avoid waiting for replacement algorithm/write during page fault Typical goal: ~5% of main memory in free page pool Sweeper process Privileged (kernel) process Scheduled whenever free page pool drops below threshold» Low watermark (sweep) vs- high watermark (goal) Sweeps through list of allocated pages doing 2 nd chance

16 Nth Chance Like second chance but If page is referenced, clear its counter and move on If page is not referenced, increment its counter» If new counter == N, select this page» Otherwise move on If N is big, we have a really good LRU approximation» But we spend a lot of time looking for pages If N == 1 we have second chance If N == 0 we have FIFO Lots more work exists on page replacement

17 Belady s Anomaly For some replacement algorithms MORE pages in main memory can lead to MORE page faults! This phenomenon is known as Belady s Anomaly Example: FIFO replacement policy Reference string: A B C D A B E A B C D E Three pages à 9 faults Four pages à 10 faults! Interesting since we would expect that adding more memory always helps

18 Thrashing Working set: collection of memory currently being used by a process If all working sets do not fit in memory à thrashing One hot page replaces another Percentage of accesses that generate page faults skyrockets Typical solution: swap out entire processes Scheduler needs to get involved Two-level scheduling policy à runnable vs memory-available Need to be fair Invoked when page fault rate exceeds some bound When swap devices are full, Linux invokes the OOM killer

19 Who should we compete against for memory? Global replacement: All pages for all processes come from single shared pool Advantage: very flexible à can globally optimize memory usage Disadvantages: Thrashing more likely, can often do just the wrong thing (e.g., replace the pages of a process about to be scheduled) Many OSes, including Linux, do this Per-process replacement: Each process has private pool of pages à competes with itself Alleviates inter-process problems, but not every process equal Need to know working set size for each process Windows kernel does this» There are Win32 API calls to set a process s minimum and maximum working set sizes

20 Demand paging Important From Today What is it? What is the effective access time? Page replacement policies Random, FIFO, Optimal, LRU, NRU, Belady s anomaly Thrashing Global vs local allocation Concept of a process s working set

Topic 14: Virtual Memory, Demand Paging, and Working Sets

Topic 14: Virtual Memory, Demand Paging, and Working Sets CS 414 : Operating Systems UNIVERSITY OF VIRGINIA Department of Computer Science Fall 2005 Topic 14: Virtual Memory, Demand Paging, and Working Sets Readings for this topic: Ch.9 Separation of the programmer

More information

Up until now we assumed that an entire program/process needed to be in memory to execute

Up until now we assumed that an entire program/process needed to be in memory to execute Lecture Overview Virtual memory Demand paging Page faults Page replacement Frame allocation Thrashing Operating Systems - June 7, 00 Virtual Memory Up until now we assumed that an entire program/process

More information

W4118: virtual memory

W4118: virtual memory W8: virtual memory Instructor: Junfeng Yang References: Modern Operating Systems ( rd edition), Operating Systems Concepts (8 th edition), previous W8, and OS at MIT, Stanford, and UWisc Background: memory

More information

Memory Management. memory hierarchy

Memory Management. memory hierarchy Memory Management Ideally programmers want memory that is large fast non volatile Memory hierarchy small amount of fast, expensive memory cache some medium-speed, medium price main memory gigabytes of

More information

Page Replacement Strategies. Jay Kothari Maxim Shevertalov CS 370: Operating Systems (Summer 2008)

Page Replacement Strategies. Jay Kothari Maxim Shevertalov CS 370: Operating Systems (Summer 2008) Page Replacement Strategies Jay Kothari (jayk@drexel.edu) Maxim Shevertalov (max@drexel.edu) CS 370: Operating Systems (Summer 2008) Page Replacement Policies Why do we care about Replacement Policy? Replacement

More information

Virtual Memory (Ch.10)

Virtual Memory (Ch.10) Virtual Memory (Ch.10)! Background! Demand Paging! Page Faults! Page Replacement! Page Replacement Algorithms! Thrashing! Strategies for Thrashing Prevention Silberschatz / OS Concepts / 6e - Chapter 10

More information

Virtual Memory. Virtual Memory

Virtual Memory. Virtual Memory Virtual Memory Gordon College Stephen Brinton Virtual Memory Background Demand Paging Process Creation Page Replacement Allocation of Frames Thrashing Demand Segmentation Operating System Examples Background

More information

CS 134: Operating Systems

CS 134: Operating Systems CS 134: Operating Systems Memory Fun with Paging CS 134: Operating Systems Memory Fun with Paging 1 / 37 Overview Cost of Faults Overview Overview Cost of Faults Algorithms Easy Approaches Realistic Approaches

More information

Virtual Memory Paging

Virtual Memory Paging COS 318: Operating Systems Virtual Memory Paging Kai Li Computer Science Department Princeton University (http://www.cs.princeton.edu/courses/cos318/) Today s Topics Paging mechanism Page replacement algorithms

More information

Virtual Memory: Demand Paging and Page Replacement

Virtual Memory: Demand Paging and Page Replacement Virtual Memory: Demand Paging and Page Replacement Problems that remain to be solved: Even with 8K page size, number of pages /process is very large. Can t afford to keep the entire page table for a process

More information

Module 10: Virtual Memory

Module 10: Virtual Memory Module 10: Virtual Memory Background Demand Paging Performance of Demand Paging Page Replacement Page-Replacement Algorithms Allocation of Frames Thrashing Other Considerations Demand Segmenation Applied

More information

CSE 120 Principles of Operating Systems

CSE 120 Principles of Operating Systems CSE 120 Principles of Operating Systems Fall 2004 Lecture 11: Page Replacement Geoffrey M. Voelker Memory Management Last lecture on memory management: Goals of memory management To provide a convenient

More information

Chapter 10: Virtual Memory. Virtual memory. Background Demand Paging Page Replacement Allocation of Frames Thrashing Operating System Example

Chapter 10: Virtual Memory. Virtual memory. Background Demand Paging Page Replacement Allocation of Frames Thrashing Operating System Example Chapter 0: Virtual Memory Background Demand Paging Page Replacement Allocation of Frames Thrashing Operating System Example 0. Virtual memory separation of logical memory from physical memory only part

More information

Last Class: Demand Paged Virtual Memory!

Last Class: Demand Paged Virtual Memory! Last Class: Demand Paged Virtual Memory! Benefits of demand paging: Virtual address space can be larger than physical address space. Processes can run without being fully loaded into memory. Processes

More information

Operating Systems. Virtual Memory

Operating Systems. Virtual Memory Operating Systems Virtual Memory Virtual Memory Topics. Memory Hierarchy. Why Virtual Memory. Virtual Memory Issues. Virtual Memory Solutions. Locality of Reference. Virtual Memory with Segmentation. Page

More information

ICS Principles of Operating Systems

ICS Principles of Operating Systems ICS 143 - Principles of Operating Systems Lectures 15 and 16 - Virtual Memory Prof. Ardalan Amiri Sani Prof. Nalini Venkatasubramanian ardalan@uci.edu nalini@ics.uci.edu Virtual Memory Background Demand

More information

Memory Management Thrashing, Segmentation and Paging

Memory Management Thrashing, Segmentation and Paging Memory Management Thrashing, Segmentation and Paging CS 416: Operating Systems Design, Spring 2011 Department of Computer Science Rutgers Sakai: 01:198:416 Sp11 (https://sakai.rutgers.edu) Summary of Page

More information

15 Demand Paging, Thrashing, Working Sets

15 Demand Paging, Thrashing, Working Sets 70 15 Demand Paging, Thrashing, Working Sets Readings for this topic: Siberschatz/Galvin, chapter 9 So far we have separated the programmer s view of memory from the system s view using a mapping mechanism.

More information

Performance Example memory access time = 100 nanoseconds swap fault overhead = 25 msec page fault rate = 1/1000 EAT = (1-p) * p * (25 msec)

Performance Example memory access time = 100 nanoseconds swap fault overhead = 25 msec page fault rate = 1/1000 EAT = (1-p) * p * (25 msec) Memory Management Outline Operating Systems Processes Memory Management Basic Paging Virtual memory Virtual Memory Motivation Demand Paging Logical address space larger than physical memory Virtual Memory

More information

Operating Systems Fall 2014 Virtual Memory, Page Faults, Demand Paging, and Page Replacement. Myungjin Lee

Operating Systems Fall 2014 Virtual Memory, Page Faults, Demand Paging, and Page Replacement. Myungjin Lee Operating Systems Fall 2014 Virtual Memory, Page Faults, Demand Paging, and Page Replacement Myungjin Lee myungjin.lee@ed.ac.uk 1 Reminder: Mechanics of address translation virtual address virtual page

More information

Chapter 9: Virtual-Memory Management

Chapter 9: Virtual-Memory Management Chapter 9: Virtual-Memory Management Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocation Kernel Memory Other

More information

Memory Management. Overview

Memory Management. Overview Memory Management 1 Overview Basic memory management Address Spaces Virtual memory Page replacement algorithms Design issues for paging systems Implementation issues Segmentation 2 1 Memory Management

More information

Chapter 9: Virtual Memory. Operating System Concepts 8 th Edition,

Chapter 9: Virtual Memory. Operating System Concepts 8 th Edition, Chapter 9: Virtual Memory, Silberschatz, Galvin and Gagne 2009 Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating

More information

Basic Page Replacement

Basic Page Replacement Basic Page Replacement 1. Find the location of the desired page on disk. Find a free frame: - If there is a free frame, use it - If there is no free frame, use a page replacement algorithm to select a

More information

Memory Management. Yücel Saygın. These slides are based on your text book and on the slides prepared by Andrew S. Tanenbaum

Memory Management. Yücel Saygın. These slides are based on your text book and on the slides prepared by Andrew S. Tanenbaum Memory Management Yücel Saygın These slides are based on your text book and on the slides prepared by Andrew S. Tanenbaum 1 Memory Management Ideally programmers want memory that is large fast non volatile

More information

Memory Management CS 447. Prof. R.K. Joshi Dept of CSE IIT Bombay

Memory Management CS 447. Prof. R.K. Joshi Dept of CSE IIT Bombay Memory Management CS 447 Prof. R.K. Joshi Dept of CSE IIT Bombay Some Simple Memory schemes Some Simple Memory schemes Some Simple Memory schemes Overlays: User level memory management (e.g. TurboPascal)

More information

Operating System Concepts 7 th Edition, Feb 22, 2005

Operating System Concepts 7 th Edition, Feb 22, 2005 Chapter 9: Virtual Memory Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating Kernel Memory Other Considerations

More information

Page replacement algorithms OS

Page replacement algorithms OS Page replacement algorithms 1 When a page fault occurs 2 OS has to choose a page to evict from memory If the page has been modified, the OS has to schedule a disk write of the page The page just read overwrites

More information

Chapter 9: Virtual Memory

Chapter 9: Virtual Memory Chapter 9: Virtual Memory Chapter 9: Virtual Memory Background Demand Paging Process Creation Page Replacement Allocation of Frames Thrashing Demand Segmentation Operating System Examples 9.2 Background

More information

Demand Paging & Page

Demand Paging & Page Demand Paging & Page Replacement CSE, Spring 9 Computer Systems http://www.cs.washington.edu/ /8/9 cse-7-virtualmemory -9 Perkins, DW Johnson and University of Washington Reading Readings and References»

More information

Virtual Memory. Reading: Silberschatz chapter 10 Reading: Stallings. chapter 8 EEL 358

Virtual Memory. Reading: Silberschatz chapter 10 Reading: Stallings. chapter 8 EEL 358 Virtual Memory Reading: Silberschatz chapter 10 Reading: Stallings chapter 8 1 Outline Introduction Advantages Thrashing Principal of Locality VM based on Paging/Segmentation Combined Paging and Segmentation

More information

Chapter 9: Virtual-Memory Management. Operating System Concepts with Java 8 th Edition

Chapter 9: Virtual-Memory Management. Operating System Concepts with Java 8 th Edition Chapter 9: Virtual-Memory Management Operating System Concepts with Java 8 th Edition 9.1 Silberschatz, Galvin and Gagne 2009 Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement

More information

csci 3411: Operating Systems

csci 3411: Operating Systems csci 3411: Operating Systems Virtual Memory II Gabriel Parmer Slides adapted from Silberschatz and West Caching Registers Cache Memory/ RAM Virtual Memory Registers Cache Memory/ RAM Disk Page Replacement

More information

Memory Management. Operating Systems. Monoprogramming without Swapping or Paging. Multiprogramming

Memory Management. Operating Systems. Monoprogramming without Swapping or Paging. Multiprogramming Operating Systems User OS Kernel & Device Drivers Interface Programs Management Management is an important resource that needs to be managed by the OS manager is the component of the OS responsible for

More information

! Background! Demand Paging! Process Creation! Page Replacement. ! Allocation of Frames! Thrashing! Demand Segmentation! Operating System Examples

! Background! Demand Paging! Process Creation! Page Replacement. ! Allocation of Frames! Thrashing! Demand Segmentation! Operating System Examples Chapter 9: Virtual Memory Background Demand Paging Process Creation Page Replacement Chapter 9: Virtual Memory Allocation of Frames Thrashing Demand Segmentation Operating System Examples Background 9.2

More information

OPERATING SYSTEM - VIRTUAL MEMORY

OPERATING SYSTEM - VIRTUAL MEMORY OPERATING SYSTEM - VIRTUAL MEMORY http://www.tutorialspoint.com/operating_system/os_virtual_memory.htm Copyright tutorialspoint.com A computer can address more memory than the amount physically installed

More information

Chapter 9: Virtual-Memory Management

Chapter 9: Virtual-Memory Management Chapter 9: Virtual-Memory Management Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocation Kernel Memory Other

More information

Lesson 6: Memory Management & Virtualization

Lesson 6: Memory Management & Virtualization Lesson 6: Memory Management & Virtualization Contents Dynamic allocation, Memory fragmentation Paging Address translation with paging Paging hardware Page table structures Segmentation Virtual memory background

More information

LOGICAL AND PHYSICAL ORGANIZATION MEMORY MANAGEMENT TECHNIQUES (CONT D)

LOGICAL AND PHYSICAL ORGANIZATION MEMORY MANAGEMENT TECHNIQUES (CONT D) MEMORY MANAGEMENT Requirements: Relocation (to different memory areas) Protection (run time, usually implemented together with relocation) Sharing (and also protection) Logical organization Physical organization

More information

SUBJECT CODE /NAME : CS6401 OPERATING SYSTEMS YEAR/SEM: II/04 QUESTION BANK

SUBJECT CODE /NAME : CS6401 OPERATING SYSTEMS YEAR/SEM: II/04 QUESTION BANK SUBJECT CODE /NAME : CS6401 OPERATING SYSTEMS YEAR/SEM: II/04 QUESTION BANK Unit-I OPERATING SYSTEMS OVERVIEW 1. Differentiate between tightly coupled systems and loosely coupled systems. 2. Define OS

More information

Silberschatz and Galvin Chapter 9

Silberschatz and Galvin Chapter 9 Silberschatz and Galvin Chapter 9 Virtual Memory CPSC Richard Furuta /6/99 Virtual memory Virtual memory permits the execution of processes that are not entirely in physical memory Programmer benefits

More information

Operating Systems (1DT020 & 1TT802) Lecture 10 Memory Management: Demand paging & page replacement. File system: Interface.

Operating Systems (1DT020 & 1TT802) Lecture 10 Memory Management: Demand paging & page replacement. File system: Interface. Operating Systems (1DT020 & 1TT802) Lecture 10 Memory Management: Demand paging & page replacement File system: Interface May 07, 2008 Léon Mugwaneza http://www.it.uu.se/edu/course/homepage/os/vt08 Goals

More information

Paging: Design Issues

Paging: Design Issues Paging: Design Issues 1! 2! Readings Silbershatz et al: 9.5-9.6 3! Outline Frame Allocation Case Studies 4! Thrashing A process causing page faults every few instructions is said to be thrashing If a process

More information

Al-Anbar University /College of Computer Lecture Eight / Virtual Memory

Al-Anbar University /College of Computer Lecture Eight / Virtual Memory 8. Virtual Memory 8.1 Background 8.2 Demand Paging 8.3 Process Creation 8.4 Page Replacement 8.5 Allocation of Frames 8.6 Thrashing 8.7 Demand Segmentation 8.8 Examples 8.1 Background Virtual memory is

More information

Operating Systems Memory Management

Operating Systems Memory Management Operating Systems Memory Management ECE 344 ECE 344 Operating Systems 1 Memory Management Contiguous Memory Allocation Paged Memory Management Virtual Memory ECE 344 Operating Systems 2 Binding of Instructions

More information

Chapter 10: Virtual Memory. Background

Chapter 10: Virtual Memory. Background Chapter 10: Virtual Memory Background Demand Paging Process Creation Page Replacement Allocation of Frames Thrashing Demand Segmentation Operating System Examples 10.1 Silberschatz, Galvin and Gagne 2003

More information

Chapter 9: Virtual Memory. Operating System Concepts 8 th Edition,

Chapter 9: Virtual Memory. Operating System Concepts 8 th Edition, Chapter 9: Virtual Memory, Silberschatz, Galvin and Gagne 2009 Chapter 9: Virtual Memory Background Demand Paging Page Replacement Thrashing 9.2 Silberschatz, Galvin and Gagne 2009 Objectives To describe

More information

Chapter 9: Virtual-Memory Management

Chapter 9: Virtual-Memory Management Chapter 9: Virtual-Memory Management Chapter 9: Virtual-Memory Management Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating Kernel Memory

More information

Chapter 9: Virtual Memory

Chapter 9: Virtual Memory Chapter 9: Virtual Memory Chapter 9: Virtual Memory Background Demand Paging Process Creation Page Replacement Allocation of Frames Thrashing Demand Segmentation Operating System Examples 9.2 Silberschatz,

More information

Lecture 4: Memory Management

Lecture 4: Memory Management Lecture 4: Memory Management Background Program must be brought into memory and placed within a process for it to be run Input queue collection of processes on the disk that are waiting to be brought into

More information

CSC501 Operating Systems Principles. Memory Management

CSC501 Operating Systems Principles. Memory Management CSC501 Operating Systems Principles Memory Management 1 Previous Lecture q Memory Management Q Segmentation Q Paging q Today s Lecture Q Lab 3 Q Page replacement algorithms Lab 3 : Demand Paging q Goal:

More information

Chapter 9 Virtual-Memory Management. Operating System Concepts Essentials 9 th Edition

Chapter 9 Virtual-Memory Management. Operating System Concepts Essentials 9 th Edition Chapter 9 Virtual-Memory Management Silberschatz, Galvin and Gagne 2013 Chapter 9: Virtual-Memory Management Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped

More information

CHAPTER 9 Exercises 9.1 Answer: 9.2 Ready Running Blocked Answer: 9.3

CHAPTER 9 Exercises 9.1 Answer: 9.2 Ready Running Blocked Answer: 9.3 CHAPTER 9 Virtual memory can be a very interesting subject since it has so many different aspects: page faults, managing the backing store, page replacement, frame allocation, thrashing, page size. The

More information

Chapter 9: Virtual Memory. Operating System Concepts 9 th Edition

Chapter 9: Virtual Memory. Operating System Concepts 9 th Edition Chapter 9: Virtual Memory Silberschatz, Galvin and Gagne 2013 Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating

More information

Virtual Memory. 4.1 Demand Paging

Virtual Memory. 4.1 Demand Paging Chapter 4 Virtual Memory All the memory management policies we have discussed so far, try to keep a number of processes in the memory simultaneously to allow multiprogramming. But they require an entire

More information

Operating Systems, 6 th ed. Test Bank Chapter 7

Operating Systems, 6 th ed. Test Bank Chapter 7 True / False Questions: Chapter 7 Memory Management 1. T / F In a multiprogramming system, main memory is divided into multiple sections: one for the operating system (resident monitor, kernel) and one

More information

Chapter 9: Virtual Memory

Chapter 9: Virtual Memory Chapter 9: Virtual Memory Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating Kernel Memory Other Considerations

More information

7. Memory Management

7. Memory Management Lecture Notes for CS347: Operating Systems Mythili Vutukuru, Department of Computer Science and Engineering, IIT Bombay 7. Memory Management 7.1 Basics of Memory Management What does main memory (RAM)

More information

CSE 513 Introduction to Operating Systems. Class 7 - Virtual Memory (2)

CSE 513 Introduction to Operating Systems. Class 7 - Virtual Memory (2) CSE 513 Introduction to Operating Systems Class 7 - Virtual Memory (2) Jonathan Walpole Dept. of Comp. Sci. and Eng. Oregon Health and Science University Key memory management issues Utilization Programmability

More information

Chapter 3 Memory Management: Virtual Memory

Chapter 3 Memory Management: Virtual Memory Understanding Operating Systems, Fifth Edition 3-1 Chapter 3 Memory Management: Virtual Memory At a Glance Instructor s Manual Table of Contents Overview Objectives s Quick Quizzes Class Discussion Topics

More information

Chapter 12. Paging an Virtual Memory Systems

Chapter 12. Paging an Virtual Memory Systems Chapter 12 Paging an Virtual Memory Systems Paging & Virtual Memory Virtual Memory - giving the illusion of more physical memory than there really is (via demand paging) Pure Paging - The total program

More information

Chapter 9: Virtual Memory

Chapter 9: Virtual Memory Chapter 9: Virtual Memory Silberschatz, Galvin and Gagne 2013! Chapter 9: Virtual Memory Background" Demand Paging" Copy-on-Write" Page Replacement" Allocation of Frames " Thrashing" Memory-Mapped Files"

More information

Sri vidya College of Engineering & Technology, Virudhunagar. CS6401- Operating System QUESTION BANK UNIT-IV

Sri vidya College of Engineering & Technology, Virudhunagar. CS6401- Operating System QUESTION BANK UNIT-IV Part-A QUESTION BANK UNIT-IV 1. What is a File? A file is a named collection of related information that is recorded on secondary storage. A file contains either programs or data. A file has certain structure

More information

Last Class: Introduction to Operating Systems. Today: OS and Computer Architecture

Last Class: Introduction to Operating Systems. Today: OS and Computer Architecture Last Class: Introduction to Operating Systems User apps OS Virtual machine interface hardware physical machine interface An operating system is the interface between the user and the architecture. History

More information

CS 31: Intro to Systems Virtual Memory. Kevin Webb Swarthmore College April 7, 2015

CS 31: Intro to Systems Virtual Memory. Kevin Webb Swarthmore College April 7, 2015 CS 31: Intro to Systems Virtual Memory Kevin Webb Swarthmore College April 7, 2015 Reading Quiz Memory Abstraction goal: make every process think it has the same memory layout. MUCH simpler for compiler

More information

III. Memory Management, Virtual Memory

III. Memory Management, Virtual Memory TDIU25: Operating Systems III. Memory Management, Virtual Memory SGG9: chapters 8 and 9 o Memory management: o contiguous allocation, fragmentation, segmentation, paging o Virtual memory: o demand paging,

More information

Deadlock Banker s Algorithm Memory management

Deadlock Banker s Algorithm Memory management Lecture 5: Deadlock Banker s Algorithm Memory management Contents Deadlock - Banker s Algorithm Memory management - history Segmentation Paging and implementation Page table Segmentation with paging Virtual

More information

VIRTUAL MEMORY MANAGEMENT, PART 3. CS124 Operating Systems Winter , Lecture 22

VIRTUAL MEMORY MANAGEMENT, PART 3. CS124 Operating Systems Winter , Lecture 22 VIRTUAL MEMORY MANAGEMENT, PART 3 CS124 Operating Systems Winter 2013-2014, Lecture 22 2 Page Allocation Policy Last time, covered a number of page replacement policies Handle case when a page must be

More information

GOJAN SCHOOL OF BUSINESS AND TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY CS2411-OPERATING SYSTEM QUESTION BANK UNIT-I (PROCESSES AND THREADS)

GOJAN SCHOOL OF BUSINESS AND TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY CS2411-OPERATING SYSTEM QUESTION BANK UNIT-I (PROCESSES AND THREADS) GOJAN SCHOOL OF BUSINESS AND TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY CS2411-OPERATING SYSTEM QUESTION BANK UNIT-I (PROCESSES AND THREADS) 1. What is an Operating system? What are the various OS

More information

CHAPTER 8 : VIRTUAL MEMORY. Introduction

CHAPTER 8 : VIRTUAL MEMORY. Introduction CHAPTER 8 : VIRTUAL MEMORY Introduction In simple paging and segmentation, we realised that we can : Load program pages or segments into frames that may not necessarily be contigous. Make memory address

More information

Operating Systems. Memory Management. Lecture 9 Michael O Boyle

Operating Systems. Memory Management. Lecture 9 Michael O Boyle Operating Systems Memory Management Lecture 9 Michael O Boyle 1 Chapter 8: Memory Management Background Logical/Virtual Address Space vs Physical Address Space Swapping Contiguous Memory Allocation Segmentation

More information

Virtual Memory. Virtual Memory. Paging. CSE 380 Computer Operating Systems. Paging (1)

Virtual Memory. Virtual Memory. Paging. CSE 380 Computer Operating Systems. Paging (1) Virtual Memory CSE 380 Computer Operating Systems Instructor: Insup Lee University of Pennsylvania Fall 2003 Lecture Note: Virtual Memory (revised version) 1 Recall: memory allocation with variable partitions

More information

CS420: Operating Systems

CS420: Operating Systems Virtual Memory James Moscola Department of Engineering & Computer Science York College of Pennsylvania Based on Operating System Concepts, 9th Edition by Silberschatz, Galvin, Gagne Background Code needs

More information

Lectures 21 : Memory Management (ii) Thu 19 Nov 2009

Lectures 21 : Memory Management (ii) Thu 19 Nov 2009 CS211: Programming and Operating Systems Lectures 21 : Memory Management (ii) Thu 19 Nov 2009 CS211 Lectures 21 : Memory Management (ii) 1/23 This afternoon... 1 Recall... Memory management 2 Contiguous

More information

University of Waterloo Midterm Examination

University of Waterloo Midterm Examination University of Waterloo Midterm Examination Spring, 2006 Student Name: Student ID Number: Section: Course Abbreviation and Number Course Title CS350 Operating Systems Sections 01 (14:30), 02 (11:30) Instructor

More information

PROCESS VIRTUAL MEMORY. CS124 Operating Systems Winter , Lecture 18

PROCESS VIRTUAL MEMORY. CS124 Operating Systems Winter , Lecture 18 PROCESS VIRTUAL MEMORY CS124 Operating Systems Winter 2013-2014, Lecture 18 2 Programs and Memory Programs perform many interactions with memory Accessing variables stored at specific memory locations

More information

CSI3131 Operating Systems Tutorial 8 Winter 2015 Virtual Memory

CSI3131 Operating Systems Tutorial 8 Winter 2015 Virtual Memory CSI11 Operating Systems Tutorial 8 Winter 015 Virtual Memory 1. Provide a short definition for each of the following terms: Page fault: Resident Set Working Set:. Describe how thrashing can occur in using

More information

William Stallings Computer Organization and Architecture

William Stallings Computer Organization and Architecture William Stallings Computer Organization and Architecture Chapter 8 Operating System Support Rev. 3.2 (2009-10) by Enrico Nardelli 8-1 Objectives and Functions Convenience Making the computer easier to

More information

Memory Management. Main memory Virtual memory

Memory Management. Main memory Virtual memory Memory Management Main memory Virtual memory Main memory Background (1) Processes need to share memory Instruction execution cycle leads to a stream of memory addresses Basic hardware CPU can only access

More information

COS 318: Operating Systems. Virtual Memory and Address Translation

COS 318: Operating Systems. Virtual Memory and Address Translation COS 318: Operating Systems Virtual Memory and Address Translation Today s Topics Midterm Results Virtual Memory Virtualization Protection Address Translation Base and bound Segmentation Paging Translation

More information

Lecture 13: Thrashing

Lecture 13: Thrashing Lecture 13: Thrashing Thrashing: exposing the lie of VM Thrashing: processes on system require more memory than it has. P1 P2 P3 Real mem Each time one page is brought in, another page, whose contents

More information

VM: The Final Frontier

VM: The Final Frontier VM: The Final Frontier Topics Clock Thrashing Working sets Learning Objectives: Demonstrate how a clock algorithm works. Define thrashing and explain how it can happen in a system (both with respect to

More information

VALLIAMMAI ENGINEERING COLLEGE

VALLIAMMAI ENGINEERING COLLEGE VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur-603203 DEPARTMENT OF INFORMATION TECHNOLOGY Academic Year: 205-6 QUESTION BANK - EVEN SEMESTER NAME OF THE SUBJECT SUBJECT CODE SEMESTER YEAR DEPARTMENT

More information

Topics. Caches and Virtual Memory. Cache Operations. Cache Operations. Write Policies on Cache Hit. Read and Write Policies.

Topics. Caches and Virtual Memory. Cache Operations. Cache Operations. Write Policies on Cache Hit. Read and Write Policies. Topics Caches and Virtual Memory CS 333 Fall 2006 Cache Operations Placement strategy Replacement strategy Read and write policy Virtual Memory Why? General overview Lots of terminology Cache Operations

More information

Agenda. Memory Management. Binding of Instructions and Data to Memory. Background. CSCI 444/544 Operating Systems Fall 2008

Agenda. Memory Management. Binding of Instructions and Data to Memory. Background. CSCI 444/544 Operating Systems Fall 2008 Agenda Background Memory Management CSCI 444/544 Operating Systems Fall 2008 Address space Static vs Dynamic allocation Contiguous vs non-contiguous allocation Background Program must be brought into memory

More information

Objectives and Functions

Objectives and Functions Objectives and Functions William Stallings Computer Organization and Architecture 6 th Edition Week 10 Operating System Support Convenience Making the computer easier to use Efficiency Allowing better

More information

Operating Systems Part M15 Virtual Memory, Shared Libraries, Microkernels, Sandboxing and Virtualization. Florina Ciorba 24 November 2015

Operating Systems Part M15 Virtual Memory, Shared Libraries, Microkernels, Sandboxing and Virtualization. Florina Ciorba 24 November 2015 Operating Systems Part M15 Virtual Memory, Shared Libraries, Microkernels, Sandboxing and Virtualization Florina Ciorba 24 November 2015 Today s Overview (Main) Memory management Shared libraries Compiling,

More information

& Data Processing 2. Exercise 3: Memory Management. Dipl.-Ing. Bogdan Marin. Universität Duisburg-Essen

& Data Processing 2. Exercise 3: Memory Management. Dipl.-Ing. Bogdan Marin. Universität Duisburg-Essen Folie a: Name & Data Processing 2 3: Memory Management Dipl.-Ing. Bogdan Marin Fakultät für Ingenieurwissenschaften Abteilung Elektro-und Informationstechnik -Technische Informatik- Objectives Memory Management

More information

CHAPTER 6 Memory. CMPS375 Class Notes (Chap06) Page 1 / 17 by Kuo-pao Yang

CHAPTER 6 Memory. CMPS375 Class Notes (Chap06) Page 1 / 17 by Kuo-pao Yang CHAPTER 6 Memory 6.1 Memory 313 6.2 Types of Memory 313 6.3 The Memory Hierarchy 315 6.3.1 Locality of Reference 318 6.4 Cache Memory 319 6.4.1 Cache Mapping Schemes 321 6.4.2 Replacement Policies 333

More information

Lecture 17: Virtual Memory II. Goals of virtual memory

Lecture 17: Virtual Memory II. Goals of virtual memory Lecture 17: Virtual Memory II Last Lecture: Introduction to virtual memory Today Review and continue virtual memory discussion Lecture 17 1 Goals of virtual memory Make it appear as if each process has:

More information

361 Computer Architecture Lecture 14: Cache Memory

361 Computer Architecture Lecture 14: Cache Memory 1 361 Computer Architecture Lecture 14 Memory cache.1 The Motivation for s Memory System Processor DRAM Motivation Large memories (DRAM) are slow Small memories (SRAM) are fast Make the average access

More information

J.B. INSTITUTE OF TECHNOLOGY,DEHRAUDN

J.B. INSTITUTE OF TECHNOLOGY,DEHRAUDN J.B. INSTITUTE OF TECHNOLOGY,DEHRAUDN Question Bank Subject Name: Operating system Subject Code: (TCS 601) Department: CS/IT Faculty Name: Kapil Joshi Year/Sem: 3 rd /6 th Designation: A.P Answer the following

More information

Memory Management and Paging. CSCI 3753 Operating Systems Spring 2005 Prof. Rick Han

Memory Management and Paging. CSCI 3753 Operating Systems Spring 2005 Prof. Rick Han Memory Management and Paging CSCI 3753 Operating Systems Spring 2005 Prof. Rick Han Announcements PA #2 due Friday March 18 11:55 pm - note extension of a day Read chapters 11 and 12 From last time...

More information

ACTS National Resource Center, Pune Question Bank Operating Systems (Unsolved)

ACTS National Resource Center, Pune Question Bank Operating Systems (Unsolved) Q.1 Fill in the blanks: (1 Mark each) 1. Single system image is obtained in case of 2. Turnaround Time refers to. 3. scheduler selects the process that is ready to execute to CPU. 4. Banker s algorithm

More information

CH 7. MAIN MEMORY. Base and Limit Registers. Memory-Management Unit (MMU) Chapter 7: Memory Management. Background. Logical vs. Physical Address Space

CH 7. MAIN MEMORY. Base and Limit Registers. Memory-Management Unit (MMU) Chapter 7: Memory Management. Background. Logical vs. Physical Address Space Chapter 7: Memory Management CH 7. MAIN MEMORY Background Swapping Contiguous Memory Allocation Paging Structure of the Page Table Segmentation adapted from textbook slides Background Base and Limit Registers

More information

The Operating System Level

The Operating System Level The Operating System Level Virtual Memory File systems Parallel processing Case studies Due 6/3: 2, 3, 18, 23 Like other levels we have studied, the OS level is built on top of the next lower layer. Like

More information

CS161: Operating Systems

CS161: Operating Systems CS161: Operating Systems Matt Welsh mdw@eecs.harvard.edu Lecture 2: OS Structure and System Calls February 6, 2007 1 Lecture Overview Protection Boundaries and Privilege Levels What makes the kernel different

More information

Sample Exam Question Answers

Sample Exam Question Answers Sample Exam Question Answers 1. Explain the structure of the OS and the role of each layer. The user communicates with the OS through a series of user programs which consist of a library of prewritten

More information

COSC243 Part 2: Operating Systems

COSC243 Part 2: Operating Systems COSC243 Part 2: Operating Systems Lecture 20: Main Memory Management Zhiyi Huang Dept. of Computer Science, University of Otago Zhiyi Huang (Otago) COSC243 Lecture 20 1 / 29 O/S/ course overview Introduction

More information

CS 61C: Great Ideas in Computer Architecture Virtual Memory Cont.

CS 61C: Great Ideas in Computer Architecture Virtual Memory Cont. CS 61C: Great Ideas in Computer Architecture Virtual Memory Cont. Instructors: Vladimir Stojanovic & Nicholas Weaver http://inst.eecs.berkeley.edu/~cs61c/ 1 Bare 5-Stage Pipeline Physical Address PC Inst.

More information