1. Background. 2. Demand Paging

Save this PDF as:
 WORD  PNG  TXT  JPG

Size: px
Start display at page:

Download "1. Background. 2. Demand Paging"

Transcription

1 COSC Operating Systems Design, Fall 2001, Byunggu Yu Chapter 10 Virtual Memory 1. Background PROBLEM: The entire process must be loaded into the memory to execute limits the size of a process (it must be smaller than the size of physical memory) limits the degree of multiprogramming SOLUTION: Virtual Memory allows the execution of processes that may not be completely in memory increases the degree of multiprogramming 2. Demand Paging 2.1 Basic Idea Demand paging: Whenever a process is swapped in, pager guesses the pages that will be used before the process is swapped out again. Then, instead of swapping in a whole process, the pager brings only those necessary pages into memory. 2.2 Implementation Page table is modified: each entry has valid-invalid bit Valid: The page is both legal and in memory Invalid: The page is not legal or not in memory Note that a page is legal if it is in the process' address space When a process is loaded into the memory to start its execution (i.e., startup): -- Frame allocation: Option #1: No physical frame is allocated (i.e., Pure Demand Paging) Option #2: Allocate some frames at process startup -- Swap space allocation: Option #1: copy the entire process image to the swap space Option #2: don't copy the process image to the swap space at process startup. Instead, write the pages to swap space as they are replaced

2 During the execution of a process (Page hit/page fault) -- CPU generates a logical memory address whose page number is i -- Read the i th entry of the page table. If the valid-invalid bit value is 1, the rest of the procedure is the same as that of Paging (i.e., page hit). -- Else (page fault) 1.Trap to the OS 2.Check the values of PTBR and PTLR of the current process to see if the page is legal 3.If the page number is illegal then terminate the current process 4.Else 4.1. Find a free frame from the free-frame list (or frame pool) 4.2.Schedule a disk operation to read the content of the i th page into the free frame. (e.g., the PCB can have the location of the ith page for non-contiguous swap space allocation or the base/limit of the process image in the swap space for contiguous swap space allocation. Various possible options) 4.3.When the read operation is completed, modify the page table (and possibly PCB) of the process 4.4.Resume the process and restart the interrupted instruction from the first step (i.e., fetch instruction). But what happens if there is no free frame in the free-frame list (frame pool)? --> Page replacement (Selecting a victim page) 3. Page Replacement 3.1 Basic Ideas In many cases, the current instruction and the related operands are required to be in the main memory to execute the instruction. Considering a multi-level pointer, the pointer values are not necessarily packed into a single page. What happens if there is no free frame when a page fault occurs? 1.Solution #1: Terminate the process 2.Solution #2: Swap out the process and free all its frames. 3.Solution #3: Find a victim page and, if necessary, write the page on the corresponding swap space disk block. Then copy the required page to the frame.

3 In this section, we discuss the solution #3. To implement the solution, we should modify Step 4.1 of the page-fault handling procedure in Section 2.2 of this lecture note. Modified Step 4.1: If there is a free frame in the frame list (or frame pool), then use it. Else Use a page-replacement algorithm to select a victim page Copy the victim page to the corresponding swap space if necessary Change the page table and the frame list (frame pool) accordingly and use the frame. Note that Step is not always necessary. We need not write back the victim page if it is a part of the code section or if it has not been modified since it was read in from the swap space. However, to accommodate this, we should modify the page table to include modify bit. Each page table entry has a modify bit. The modify bit is set whenever any word or byte in the corresponding page is changed, indicating that the page has been modified. Some systems (e.g., Linux and the variants) maintain a separate frame table (frequently called page frame pool). This frame table includes m entries, where m is the total number of physical frames constituting the physical memory. Each entry of the table represents the status of the corresponding frame. For example, we can store modify bit, lock bit and free bit that can tell us whether the frame content need to be written back to the swap space, whether the page in the frame can be selected as a victim frame for a page replacement, and whether the frame is free or not. 3.2 Page-Replacement Algorithms * FIFO (First-In First-Out) Algorithm The victim frame (the frame that contains the victim page) is the oldest one. Implementation: Additional FIFO queue of allocated frames is needed. -- Victim frame is the head of the FIFO queue -- New frame is the tail of the FIFO queue Global allocation: Need a global FIFO queue. Possibly, we can implement a FIFO queue in the frame table. Local allocation: Need one FIFO queue for each process. Possibly, we can implement the page table as FIFO queue. * Optimal Algorithm for comparison study Victim frame is the one that will not be used for the longest period of time. Implementation: Almost impossible to implement, since it requires the future knowledge of the memory references. However, we can use it for comparative

4 performance evaluation: When you propose a page-replacement algorithm, you can compare it with this optimal algorithm. * LRU (Least Recently Used) Algorithm Victim frame is the one that has not been accessed for the longest period of time. Implementation: Use Counter or Stack Counter: Modify the page table (local counter) or frame table (global counter) each entry has a time-of-use field. Whenever a reference to the frame is made, the content of the clock (or counter) register is copied to the timeof-use field. In this way, we have the time of the last reference to the frame. The one who has the smallest time-of-use value is the victim. Problem #1: H/W counter or clock is required Problem #2: Must search the page table to find the LRU frame (note, if a list (LRU list) is used, the structure must be updated whenever there is a memory access). Problem #3: time-of-use must be updated for every page reference (overhead) Stack: Additional stack of frame (or page) numbers. The bottom of the stack is the LRU frame (or page). Problem: Stack must be updated for every page reference (overhead) Without the H/W support (e.g., counter or stack registers), the LRU algorithm is very slow, since the time-of-use or the stack must be updated very frequently (additional memory accesses). Many computer systems provide a reference bit for each page or frame. The bit associated each page reference is set to one by the H/W. The following three variants of the LRU algorithm use this minimum H/W support. * LRU Approximation Algorithm #1: Additional-Reference-Byte Algorithm Victim: the frame indicated by the page (or frame) entry whose 8-bit byte (reference-byte) value is the smallest one. Each page table (or frame table) entry has reference-byte (8-bit byte). At regular interval (e.g., 100 milliseconds), the timer interrupt routine writes the most recent reference bit into the high-order bit (MSB) of the 8-bit byte, shifting the other bits right 1 bit, discarding the low-order bit (LSB). --> the history of page accesses during the last eight time intervals. e.g., A page (or frame) with a reference-byte value of has been used more recently than the page that is associated with * LRU Approximation Algorithm #2: Second-Chance Algorithm Victim: The first page (or frame) in the FIFO queue whose reference-bit is zero. The FIFO queue is a circular queue. That is, the tail of the queue points to the head of the queue. To find the victim, OS scans the queue from the last stop point in a circular fashion until it finds a page whose current reference bit is zero

5 (victim page). As the pointer advances, it sets the reference bits to zero (see Figure in p. 342). * LRU Approximation Algorithm #3: Enhanced Second-Chance Algorithm Victim: Scan the entire circular queue possibly several times and find the first page (or frame) that is in the lowest class (class is <reference bit, modify bit>. see the four classes of nonempty frames in P.343) --> by considering the modify-bit, we can reduce the number of write operations (disk I/Os) on the swap space. * We skip Counting Algorithm and Page Buffering Algorithm 4. Allocation of Frames 4.1 Minimum/Maximum Number of Frames The maximum number of frames per process is defined by the amount of available physical memory. The minimum number of frames per process is defined by the underlying computer architecture. For example, if the architecture allows up to 15 levels of indirect memory addressing (you can imagine the maximum number of * s in the front of a pointer type variable in C), the minimum number of frames should be Equal Allocation and Proportional Allocation There are n processes and m physical frames. Equal Allocation: Each process has m/n frames Proportional Allocation: Each process has si/s*m frames, where si is the size of the process and S is the total amount of address space of the n processes. That is, a larger process gets a larger number of frames. 4.3 Global allocation vs. Local allocation Global allocation: select the victim frame from the frames of the physical memory. Local allocation: select the victim frame from the current process' frames.

6 5. Thrashing Trashing: Very high paging activity Too many processes in memory --> # of allocated frames < its locality --> processes spend more time on paging than executing instructions. --> The process is in a thrashing State. 5.1 Solution #1: Local Replacement Algorithm: A process cannot steal a frame from another process. --> no global thrashing (no propagation) --> Increase I/O requests from the thrashing process --> decrease the system performance. 5.2 Solution #2: Locality Model with Working-Set Model D=WSSi, where WSSi is the number of different pages in the most recent memory accesses of Pi. The value represents the average number of memory accesses by a process in a single locality. If D > m, select a victim process, suspend it, and swap it out. 5.3 Solution #3: PFF (Page-Fault Frequency) strategy Predetermined upper bound and lower bound of page-fault rate. When there is a free frame: If the current process' page-fault rate exceeds the upper bound then allocate a frame to the current process. If the current process' page-fault rate falls below the lower bound then remove a frame from the current process. When there is no free frame: If the current process' page-fault rate exceeds the upper bound then select a victim process and suspend it. If the current process' page-fault rate falls below the lower bound then remove a frame from the current process. 6. Other Considerations 6.1 Prepaging When we start or restart a process, pager brings enough number of pages, which constitute a single locality, into the main memory at once. 6.2 Page Size (usually 1K, 2K, 4K, or 8K-byte) A smaller page size --> increases the size of page table, --> decreases the internal fragments, --> increases the number of disk I/Os, --> improves the locality representation, and

7 --> increases the page-fault rate. A larger page size --> decreases the size of page tables, --> increases the internal fragments, --> decreases the number of disk I/Os, --> aggravates the locality representation, and --> decreases the page-fault rate. 6.3 I/O Interlock Process 1 requests a disk I/O to read one data page from the disk into Frame 5. CPU switches to Process 2 Process 2 generates a page-fault Frame 5 is selected as a victim frame by a global allocation strategy Process 2 uses Frame 5 CPU switches back to Process 1 Process 1 accesses Frame 5 What happens? --> Solution: Each entry of page table or frame table has lock-bit. Process 1 can lock Frame 5. If the frame is locked, it cannot be selected for replacement. 6.6 Real-Time Processing Virtual memory is not a good technique for real-time systems, since the page-fault service and disk I/O operations are expensive. Solaris2: allow both real-time and time-sharing computing within a system --> allows a process to tell the system which pages are important to that process. A real-time process requests enough number of important frames and lock the frames. --> But other nearthrashing processes can reduce the I/O response time --> Priority based scheduling -->...

Operating System Concepts

Operating System Concepts Chapter 9: Virtual-Memory Management 9.1 Silberschatz, Galvin and Gagne 2005 Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped

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 Allocating

More information

Chapter 9: Virtual Memory

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

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 Operating System Examples 10.1 Background Virtual memory separation of user logical

More information

Principles of Operating Systems

Principles of Operating Systems Principles of Operating Systems Lecture 21-23 - Virtual Memory Ardalan Amiri Sani (ardalan@uci.edu) [lecture slides contains some content adapted from previous slides by Prof. Nalini Venkatasubramanian,

More information

Chapter 10: Virtual Memory. Background. Demand Paging. Valid-Invalid Bit. Virtual Memory That is Larger Than Physical Memory

Chapter 10: Virtual Memory. Background. Demand Paging. Valid-Invalid Bit. Virtual Memory That is Larger Than Physical Memory Chapter 0: Virtual Memory Background Background Demand Paging Process Creation Page Replacement Allocation of Frames Thrashing Operating System Examples Virtual memory separation of user logical memory

More information

Background. Demand Paging. valid-invalid bit. Tevfik Koşar. CSC Operating Systems Spring 2007

Background. Demand Paging. valid-invalid bit. Tevfik Koşar. CSC Operating Systems Spring 2007 CSC 0 - Operating Systems Spring 007 Lecture - XIII Virtual Memory Tevfik Koşar Background Virtual memory separation of user logical memory from physical memory. Only part of the program needs to be in

More information

Where are we in the course?

Where are we in the course? Previous Lectures Memory Management Approaches Allocate contiguous memory for the whole process Use paging (map fixed size logical pages to physical frames) Use segmentation (user s view of address space

More information

CS6401- Operating System UNIT-III STORAGE MANAGEMENT

CS6401- Operating System UNIT-III STORAGE MANAGEMENT UNIT-III STORAGE MANAGEMENT Memory Management: Background In general, to rum a program, it must be brought into memory. Input queue collection of processes on the disk that are waiting to be brought into

More information

Chapter 9: Virtual Memory. Chapter 9: Virtual Memory. Objectives. Background. Virtual-address address Space

Chapter 9: Virtual Memory. Chapter 9: Virtual Memory. Objectives. Background. Virtual-address address Space 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

Chapter 8: Virtual Memory. Operating System Concepts

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

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

Virtual Memory COMPSCI 386

Virtual Memory COMPSCI 386 Virtual Memory COMPSCI 386 Motivation An instruction to be executed must be in physical memory, but there may not be enough space for all ready processes. Typically the entire program is not needed. Exception

More information

Page Replacement. 3/9/07 CSE 30341: Operating Systems Principles

Page Replacement. 3/9/07 CSE 30341: Operating Systems Principles Page Replacement page 1 Page Replacement Algorithms Want lowest page-fault rate Evaluate algorithm by running it on a particular string of memory references (reference string) and computing the number

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. Virtual Memory. Demand Paging. valid-invalid bit. Virtual Memory Larger than Physical Memory

Virtual Memory. Virtual Memory. Demand Paging. valid-invalid bit. Virtual Memory Larger than Physical Memory Virtual Memory Virtual Memory CSCI Operating Systems Design Department of Computer Science Virtual memory separation of user logical memory from physical memory. Only part of the program needs to be in

More information

Background. Virtual Memory (2/2) Demand Paging Example. First-In-First-Out (FIFO) Algorithm. Page Replacement Algorithms. Performance of Demand Paging

Background. Virtual Memory (2/2) Demand Paging Example. First-In-First-Out (FIFO) Algorithm. Page Replacement Algorithms. Performance of Demand Paging Virtual Memory (/) Background Page Replacement Allocation of Frames Thrashing Background Virtual memory separation of user logical memory from physical memory. Only part of the program needs to be in memory

More information

Virtual Memory. CSCI 315 Operating Systems Design Department of Computer Science

Virtual Memory. CSCI 315 Operating Systems Design Department of Computer Science Virtual Memory CSCI 315 Operating Systems Design Department of Computer Science Notice: The slides for this lecture were based on those Operating Systems Concepts, 9th ed., by Silberschatz, Galvin, and

More information

Chapter 8: Virtual Memory. Operating System Concepts Essentials 2 nd Edition

Chapter 8: Virtual Memory. Operating System Concepts Essentials 2 nd Edition Chapter 8: Virtual Memory Silberschatz, Galvin and Gagne 2013 Chapter 8: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating

More information

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

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

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

Chapter 9: Virtual Memory

Chapter 9: Virtual Memory Chapter 9: Virtual Memory Multiprogramming Memory Management so far 1. Dynamic Loading The main Program gets loaded into memory Routines are stored in Relocatable Load format on disk As main program (or

More information

Virtual Memory. CSCI 315 Operating Systems Design Department of Computer Science

Virtual Memory. CSCI 315 Operating Systems Design Department of Computer Science Virtual Memory CSCI 315 Operating Systems Design Department of Computer Science Notice: The slides for this lecture have been largely based on those from an earlier edition of the course text Operating

More information

OPERATING SYSTEM. Chapter 9: Virtual Memory

OPERATING SYSTEM. Chapter 9: Virtual Memory OPERATING SYSTEM 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

More information

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

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

More information

!! What is virtual memory and when is it useful? !! What is demand paging? !! When should pages in memory be replaced?

!! What is virtual memory and when is it useful? !! What is demand paging? !! When should pages in memory be replaced? Chapter 10: Virtual Memory Questions? CSCI [4 6] 730 Operating Systems Virtual Memory!! What is virtual memory and when is it useful?!! What is demand paging?!! When should pages in memory be replaced?!!

More information

Lecture 17. Edited from slides for Operating System Concepts by Silberschatz, Galvin, Gagne

Lecture 17. Edited from slides for Operating System Concepts by Silberschatz, Galvin, Gagne Lecture 17 Edited from slides for Operating System Concepts by Silberschatz, Galvin, Gagne Page Replacement Algorithms Last Lecture: FIFO Optimal Page Replacement LRU LRU Approximation Additional-Reference-Bits

More information

Operating System - Virtual Memory

Operating System - Virtual Memory Operating System - Virtual Memory Virtual memory is a technique that allows the execution of processes which are not completely available in memory. The main visible advantage of this scheme is that programs

More information

Memory Management. To improve CPU utilization in a multiprogramming environment we need multiple programs in main memory at the same time.

Memory Management. To improve CPU utilization in a multiprogramming environment we need multiple programs in main memory at the same time. Memory Management To improve CPU utilization in a multiprogramming environment we need multiple programs in main memory at the same time. Basic CPUs and Physical Memory CPU cache Physical memory

More information

Memory Management Cache Base and Limit Registers base limit Binding of Instructions and Data to Memory Compile time absolute code Load time

Memory Management Cache Base and Limit Registers base limit Binding of Instructions and Data to Memory Compile time absolute code Load time Memory Management To provide a detailed description of various ways of organizing memory hardware To discuss various memory-management techniques, including paging and segmentation To provide a detailed

More information

Addresses in the source program are generally symbolic. A compiler will typically bind these symbolic addresses to re-locatable addresses.

Addresses in the source program are generally symbolic. A compiler will typically bind these symbolic addresses to re-locatable addresses. 1 Memory Management Address Binding The normal procedures is to select one of the processes in the input queue and to load that process into memory. As the process executed, it accesses instructions and

More information

CS370 Operating Systems

CS370 Operating Systems CS370 Operating Systems Colorado State University Yashwant K Malaiya Fall 2016 Lecture 33 Virtual Memory Slides based on Text by Silberschatz, Galvin, Gagne Various sources 1 1 FAQ How does the virtual

More information

Memory management, part 2: outline

Memory management, part 2: outline Memory management, part 2: outline Page replacement algorithms Modeling PR algorithms o Working-set model and algorithms Virtual memory implementation issues 1 Page Replacement Algorithms Page fault forces

More information

Swapping. Operating Systems I. Swapping. Motivation. Paging Implementation. Demand Paging. Active processes use more physical memory than system has

Swapping. Operating Systems I. Swapping. Motivation. Paging Implementation. Demand Paging. Active processes use more physical memory than system has Swapping Active processes use more physical memory than system has Operating Systems I Address Binding can be fixed or relocatable at runtime Swap out P P Virtual Memory OS Backing Store (Swap Space) Main

More information

Operating Systems Lecture 6: Memory Management II

Operating Systems Lecture 6: Memory Management II CSCI-GA.2250-001 Operating Systems Lecture 6: Memory Management II Hubertus Franke frankeh@cims.nyu.edu What is the problem? Not enough memory Have enough memory is not possible with current technology

More information

Chapter 8 Virtual Memory

Chapter 8 Virtual Memory Chapter 8 Virtual Memory Contents Hardware and control structures Operating system software Unix and Solaris memory management Linux memory management Windows 2000 memory management Characteristics of

More information

Virtual Memory: Page Replacement. CSSE 332 Operating Systems Rose-Hulman Institute of Technology

Virtual Memory: Page Replacement. CSSE 332 Operating Systems Rose-Hulman Institute of Technology Virtual Memory: Page Replacement CSSE 332 Operating Systems Rose-Hulman Institute of Technology Announcements Project E & presentation are due Wednesday Team reflections due Monday, May 19 The need for

More information

Memory Management Outline. Operating Systems. Motivation. Paging Implementation. Accessing Invalid Pages. Performance of Demand Paging

Memory Management Outline. Operating Systems. Motivation. Paging Implementation. Accessing Invalid Pages. Performance of Demand Paging Memory Management Outline Operating Systems Processes (done) Memory Management Basic (done) Paging (done) Virtual memory Virtual Memory (Chapter.) Motivation Logical address space larger than physical

More information

Chapters 9 & 10: Memory Management and Virtual Memory

Chapters 9 & 10: Memory Management and Virtual Memory Chapters 9 & 10: Memory Management and Virtual Memory Important concepts (for final, projects, papers) addressing: physical/absolute, logical/relative/virtual overlays swapping and paging memory protection

More information

Memory Management. Virtual Memory. By : Kaushik Vaghani. Prepared By : Kaushik Vaghani

Memory Management. Virtual Memory. By : Kaushik Vaghani. Prepared By : Kaushik Vaghani Memory Management Virtual Memory By : Kaushik Vaghani Virtual Memory Background Page Fault Dirty Page / Dirty Bit Demand Paging Copy-on-Write Page Replacement Objectives To describe the benefits of a virtual

More information

Chapter 8 & Chapter 9 Main Memory & Virtual Memory

Chapter 8 & Chapter 9 Main Memory & Virtual Memory Chapter 8 & Chapter 9 Main Memory & Virtual Memory 1. Various ways of organizing memory hardware. 2. Memory-management techniques: 1. Paging 2. Segmentation. Introduction Memory consists of a large array

More information

stack Two-dimensional logical addresses Fixed Allocation Binary Page Table

stack Two-dimensional logical addresses Fixed Allocation Binary Page Table Question # 1 of 10 ( Start time: 07:24:13 AM ) Total Marks: 1 LRU page replacement algorithm can be implemented by counter stack linked list all of the given options Question # 2 of 10 ( Start time: 07:25:28

More information

CS370 Operating Systems

CS370 Operating Systems CS370 Operating Systems Colorado State University Yashwant K Malaiya Fall 2016 Lecture 32 Virtual Memory Slides based on Text by Silberschatz, Galvin, Gagne Various sources 1 1 Questions for you What is

More information

CS450/550 Operating Systems

CS450/550 Operating Systems CS450/550 Operating Systems Lecture 4 memory Palden Lama Department of Computer Science CS450/550 Memory.1 Review: Summary of Chapter 3 Deadlocks and its modeling Deadlock detection Deadlock recovery Deadlock

More information

Virtual Memory CHAPTER CHAPTER OBJECTIVES. 8.1 Background

Virtual Memory CHAPTER CHAPTER OBJECTIVES. 8.1 Background Virtual Memory 8 CHAPTER In Chapter 7, we discussed various memory-management strategies used in computer systems. All these strategies have the same goal: to keep many processes in memory simultaneously

More information

Chapter 8 Virtual Memory

Chapter 8 Virtual Memory Operating Systems: Internals and Design Principles Chapter 8 Virtual Memory Seventh Edition William Stallings Modified by Rana Forsati for CSE 410 Outline Principle of locality Paging - Effect of page

More information

CS510 Operating System Foundations. Jonathan Walpole

CS510 Operating System Foundations. Jonathan Walpole CS510 Operating System Foundations Jonathan Walpole Page Replacement Page Replacement Assume a normal page table (e.g., BLITZ) User-program is executing A PageInvalidFault occurs! - The page needed is

More information

ECE 7650 Scalable and Secure Internet Services and Architecture ---- A Systems Perspective. Part I: Operating system overview: Memory Management

ECE 7650 Scalable and Secure Internet Services and Architecture ---- A Systems Perspective. Part I: Operating system overview: Memory Management ECE 7650 Scalable and Secure Internet Services and Architecture ---- A Systems Perspective Part I: Operating system overview: Memory Management 1 Hardware background The role of primary memory Program

More information

Even in those cases where the entire program is needed, it may not all be needed at the same time (such is the case with overlays, for example).

Even in those cases where the entire program is needed, it may not all be needed at the same time (such is the case with overlays, for example). Chapter 10 VIRTUAL MEMORY In Chapter 9, we discussed various memory-management strategies used in computer systems. All these strategies have the same goal: to keep many processes in memory simultaneously

More information

Role of OS in virtual memory management

Role of OS in virtual memory management Role of OS in virtual memory management Role of OS memory management Design of memory-management portion of OS depends on 3 fundamental areas of choice Whether to use virtual memory or not Whether to use

More information

Basic Memory Management

Basic Memory Management Basic Memory Management CS 256/456 Dept. of Computer Science, University of Rochester 10/15/14 CSC 2/456 1 Basic Memory Management Program must be brought into memory and placed within a process for it

More information

CS 4410 Operating Systems. Page Replacement (2) Summer 2016 Cornell University

CS 4410 Operating Systems. Page Replacement (2) Summer 2016 Cornell University CS 4410 Operating Systems Page Replacement (2) Summer 2016 Cornell University Today Algorithm that approximates the OPT replacement algorithm. 2 Least Recently Used (LRU) Page Replacement A recently used

More information

MEMORY MANAGEMENT/1 CS 409, FALL 2013

MEMORY MANAGEMENT/1 CS 409, FALL 2013 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

Virtual Memory. Chapter 8

Virtual Memory. Chapter 8 Virtual Memory 1 Chapter 8 Characteristics of Paging and Segmentation Memory references are dynamically translated into physical addresses at run time E.g., process may be swapped in and out of main memory

More information

CS 333 Introduction to Operating Systems. Class 14 Page Replacement. Jonathan Walpole Computer Science Portland State University

CS 333 Introduction to Operating Systems. Class 14 Page Replacement. Jonathan Walpole Computer Science Portland State University CS 333 Introduction to Operating Systems Class 14 Page Replacement Jonathan Walpole Computer Science Portland State University Page replacement Assume a normal page table (e.g., BLITZ) User-program is

More information

Lecture 14 Page Replacement Policies

Lecture 14 Page Replacement Policies CS 423 Operating Systems Design Lecture 14 Page Replacement Policies Klara Nahrstedt Fall 2011 Based on slides by YY Zhou and Andrew S. Tanenbaum Overview Administrative Issues Page Replacement Policies

More information

Modeling Page Replacement: Stack Algorithms. Design Issues for Paging Systems

Modeling Page Replacement: Stack Algorithms. Design Issues for Paging Systems Modeling Page Replacement: Stack Algorithms 7 4 6 5 State of memory array, M, after each item in reference string is processed CS450/550 Memory.45 Design Issues for Paging Systems Local page replacement

More information

Operating Systems Virtual Memory. Lecture 11 Michael O Boyle

Operating Systems Virtual Memory. Lecture 11 Michael O Boyle Operating Systems Virtual Memory Lecture 11 Michael O Boyle 1 Paged virtual memory Allows a larger logical address space than physical memory All pages of address space do not need to be in memory the

More information

Chapter 4 Memory Management

Chapter 4 Memory Management Chapter 4 Memory Management 4.1 Basic memory management 4.2 Swapping 4.3 Virtual memory 4.4 Page replacement algorithms 4.5 Modeling page replacement algorithms 4.6 Design issues for paging systems 4.7

More information

! What is virtual memory and when is it useful? ! What is demand paging? ! What pages should be. ! What is the working set model?

! What is virtual memory and when is it useful? ! What is demand paging? ! What pages should be. ! What is the working set model? Virtual Memory Questions? CSCI [4 6] 730 Operating Systems Virtual Memory! What is virtual memory and when is it useful?! What is demand paging?! What pages should be» resident in memory, and» which should

More information

instruction is 6 bytes, might span 2 pages 2 pages to handle from 2 pages to handle to Two major allocation schemes

instruction is 6 bytes, might span 2 pages 2 pages to handle from 2 pages to handle to Two major allocation schemes Allocation of Frames How should the OS distribute the frames among the various processes? Each process needs minimum number of pages - at least the minimum number of pages required for a single assembly

More information

Chapter 8 Virtual Memory

Chapter 8 Virtual Memory Operating Systems: Internals and Design Principles Chapter 8 Virtual Memory Seventh Edition William Stallings Operating Systems: Internals and Design Principles You re gonna need a bigger boat. Steven

More information

Week 2: Tiina Niklander

Week 2: Tiina Niklander Virtual memory Operations and policies Chapters 3.4. 3.6 Week 2: 17.9.2009 Tiina Niklander 1 Policies and methods Fetch policy (Noutopolitiikka) When to load page to memory? Placement policy (Sijoituspolitiikka

More information

Chapter 4: Memory Management. Part 1: Mechanisms for Managing Memory

Chapter 4: Memory Management. Part 1: Mechanisms for Managing Memory Chapter 4: Memory Management Part 1: Mechanisms for Managing Memory Memory management Basic memory management Swapping Virtual memory Page replacement algorithms Modeling page replacement algorithms Design

More information

Virtual Memory Design and Implementation

Virtual Memory Design and Implementation Virtual Memory Design and Implementation To do q Page replacement algorithms q Design and implementation issues q Next: Last on virtualization VMMs Loading pages When should the OS load pages? On demand

More information

VIRTUAL MEMORY READING: CHAPTER 9

VIRTUAL MEMORY READING: CHAPTER 9 VIRTUAL MEMORY READING: CHAPTER 9 9 MEMORY HIERARCHY Core! Processor! Core! Caching! Main! Memory! (DRAM)!! Caching!! Secondary Storage (SSD)!!!! Secondary Storage (Disk)! L cache exclusive to a single

More information

ECE7995 Caching and Prefetching Techniques in Computer Systems. Lecture 8: Buffer Cache in Main Memory (I)

ECE7995 Caching and Prefetching Techniques in Computer Systems. Lecture 8: Buffer Cache in Main Memory (I) ECE7995 Caching and Prefetching Techniques in Computer Systems Lecture 8: Buffer Cache in Main Memory (I) 1 Review: The Memory Hierarchy Take advantage of the principle of locality to present the user

More information

Memory Management. Chapter 4 Memory Management. Multiprogramming with Fixed Partitions. Ideally programmers want memory that is.

Memory Management. Chapter 4 Memory Management. Multiprogramming with Fixed Partitions. Ideally programmers want memory that is. Chapter 4 Memory Management Ideally programmers want memory that is Memory Management large fast non volatile 4.1 Basic memory management 4.2 Swapping 4.3 Virtual memory 4.4 Page replacement algorithms

More information

Last class: Today: Paging. Virtual Memory

Last class: Today: Paging. Virtual Memory Last class: Paging Today: Virtual Memory Virtual Memory What if programs require more memory than available physical memory? Use overlays ifficult to program though! Virtual Memory. Supports programs that

More information

Chapter 4 Memory Management. Memory Management

Chapter 4 Memory Management. Memory Management Chapter 4 Memory Management 4.1 Basic memory management 4.2 Swapping 4.3 Virtual memory 4.4 Page replacement algorithms 4.5 Modeling page replacement algorithms 4.6 Design issues for paging systems 4.7

More information

The Virtual Memory Abstraction. Memory Management. Address spaces: Physical and Virtual. Address Translation

The Virtual Memory Abstraction. Memory Management. Address spaces: Physical and Virtual. Address Translation The Virtual Memory Abstraction Memory Management Physical Memory Unprotected address space Limited size Shared physical frames Easy to share data Virtual Memory Programs are isolated Arbitrary size All

More information

Memory Allocation. Copyright : University of Illinois CS 241 Staff 1

Memory Allocation. Copyright : University of Illinois CS 241 Staff 1 Memory Allocation Copyright : University of Illinois CS 241 Staff 1 Allocation of Page Frames Scenario Several physical pages allocated to processes A, B, and C. Process B page faults. Which page should

More information

Operating Systems CSE 410, Spring Virtual Memory. Stephen Wagner Michigan State University

Operating Systems CSE 410, Spring Virtual Memory. Stephen Wagner Michigan State University Operating Systems CSE 410, Spring 2004 Virtual Memory Stephen Wagner Michigan State University Virtual Memory Provide User an address space that is larger than main memory Secondary storage is used to

More information

Virtual Memory B: Objec5ves

Virtual Memory B: Objec5ves Virtual Memory B: Objec5ves Benefits of a virtual memory system" Demand paging, page-replacement algorithms, and allocation of page frames" The working-set model" Relationship between shared memory and

More information

Operating Systems. IV. Memory Management

Operating Systems. IV. Memory Management Operating Systems IV. Memory Management Ludovic Apvrille ludovic.apvrille@telecom-paristech.fr Eurecom, office 470 http://soc.eurecom.fr/os/ @OS Eurecom Outline Basics of Memory Management Hardware Architecture

More information

Topics: Virtual Memory (SGG, Chapter 09) CS 3733 Operating Systems

Topics: Virtual Memory (SGG, Chapter 09) CS 3733 Operating Systems Topics: Virtual Memory (SGG, Chapter 09) 9.1-9.7 CS 3733 Operating Systems Instructor: Dr. Turgay Korkmaz Department Computer Science The University of Texas at San Antonio Office: NPB 3.330 Phone: (210)

More information

Operating System Principles: Memory Management Swapping, Paging, and Virtual Memory CS 111. Operating Systems Peter Reiher

Operating System Principles: Memory Management Swapping, Paging, and Virtual Memory CS 111. Operating Systems Peter Reiher Operating System Principles: Memory Management Swapping, Paging, and Virtual Memory Operating Systems Peter Reiher Page 1 Outline Swapping Paging Virtual memory Page 2 Swapping What if we don t have enough

More information

Memory Management: Virtual Memory and Paging CS 111. Operating Systems Peter Reiher

Memory Management: Virtual Memory and Paging CS 111. Operating Systems Peter Reiher Memory Management: Virtual Memory and Paging Operating Systems Peter Reiher Page 1 Outline Paging Swapping and demand paging Virtual memory Page 2 Paging What is paging? What problem does it solve? How

More information

ECE519 Advanced Operating Systems

ECE519 Advanced Operating Systems IT 540 Operating Systems ECE519 Advanced Operating Systems Prof. Dr. Hasan Hüseyin BALIK (8 th Week) (Advanced) Operating Systems 8. Virtual Memory 8. Outline Hardware and Control Structures Operating

More information

Chapter 8: Memory- Management Strategies. Operating System Concepts 9 th Edition

Chapter 8: Memory- Management Strategies. Operating System Concepts 9 th Edition Chapter 8: Memory- Management Strategies Operating System Concepts 9 th Edition Silberschatz, Galvin and Gagne 2013 Chapter 8: Memory Management Strategies Background Swapping Contiguous Memory Allocation

More information

Chapter 8: Memory- Management Strategies

Chapter 8: Memory- Management Strategies Chapter 8: Memory Management Strategies Chapter 8: Memory- Management Strategies Background Swapping Contiguous Memory Allocation Segmentation Paging Structure of the Page Table Example: The Intel 32 and

More information

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

Chapter 8: Main Memory Chapter 9: Virtual Memory. Operating System Concepts 9th Edition Chapter 8: Main Memory Chapter 9: Virtual Memory Dr Prabhaker Mateti, CEG 4350 edition This collection is the combined edition of slides for Chapters 8 and 9 of SG, with several slides deleted or modified.

More information

Memory Organization MEMORY ORGANIZATION. Memory Hierarchy. Main Memory. Auxiliary Memory. Associative Memory. Cache Memory.

Memory Organization MEMORY ORGANIZATION. Memory Hierarchy. Main Memory. Auxiliary Memory. Associative Memory. Cache Memory. MEMORY ORGANIZATION Memory Hierarchy Main Memory Auxiliary Memory Associative Memory Cache Memory Virtual Memory MEMORY HIERARCHY Memory Hierarchy Memory Hierarchy is to obtain the highest possible access

More information

Chapter 7: Main Memory. Operating System Concepts Essentials 8 th Edition

Chapter 7: Main Memory. Operating System Concepts Essentials 8 th Edition Chapter 7: Main Memory Operating System Concepts Essentials 8 th Edition Silberschatz, Galvin and Gagne 2011 Chapter 7: Memory Management Background Swapping Contiguous Memory Allocation Paging Structure

More information

Operating Systems. User OS. Kernel & Device Drivers. Interface Programs. Memory Management

Operating Systems. User OS. Kernel & Device Drivers. Interface Programs. Memory Management Operating Systems User OS Kernel & Device Drivers Interface Programs Management Brian Mitchell (bmitchel@mcs.drexel.edu) - Operating Systems 1 Management is an important resource that needs to be managed

More information

Memory Management Virtual Memory

Memory Management Virtual Memory Memory Management Virtual Memory Part of A3 course (by Theo Schouten) Biniam Gebremichael http://www.cs.ru.nl/~biniam/ Office: A6004 April 4 2005 Content Virtual memory Definition Advantage and challenges

More information

Memory Management. CSCI 315 Operating Systems Design Department of Computer Science

Memory Management. CSCI 315 Operating Systems Design Department of Computer Science Memory Management CSCI 315 Operating Systems Design Department of Computer Science Notice: The slides for this lecture are based on those from Operating Systems Concepts, 9th ed., by Silberschatz, Galvin,

More information

Virtual Memory Design and Implementation

Virtual Memory Design and Implementation Virtual Memory Design and Implementation Today! Page replacement algorithms! Some design and implementation issues Next! Last on virtualization VMMs How can any of this work?!?!! Locality Temporal locality

More information

CHAPTER 8 - MEMORY MANAGEMENT STRATEGIES

CHAPTER 8 - MEMORY MANAGEMENT STRATEGIES CHAPTER 8 - MEMORY MANAGEMENT STRATEGIES OBJECTIVES Detailed description of various ways of organizing memory hardware Various memory-management techniques, including paging and segmentation To provide

More information

Operating System 1 (ECS-501)

Operating System 1 (ECS-501) Operating System 1 (ECS-501) Unit- IV Memory Management 1.1 Bare Machine: 1.1.1 Introduction: It has the ability to recover the operating system of a machine to the identical state it was at a given point

More information

Chapter 8: Main Memory. Operating System Concepts 9 th Edition

Chapter 8: Main Memory. Operating System Concepts 9 th Edition Chapter 8: Main Memory Silberschatz, Galvin and Gagne 2013 Chapter 8: Memory Management Background Swapping Contiguous Memory Allocation Segmentation Paging Structure of the Page Table Example: The Intel

More information

Unit 2 Buffer Pool Management

Unit 2 Buffer Pool Management Unit 2 Buffer Pool Management Based on: Sections 9.4, 9.4.1, 9.4.2 of Ramakrishnan & Gehrke (text); Silberschatz, et. al. ( Operating System Concepts ); Other sources Original slides by Ed Knorr; Updates

More information

Memory Management. Memory Management

Memory Management. Memory Management Memory Management Gordon College Stephen Brinton Memory Management Background Swapping Contiguous Allocation Paging Segmentation Segmentation with Paging 1 Background Program must be brought into memory

More information

Paging and Page Replacement Algorithms

Paging and Page Replacement Algorithms Paging and Page Replacement Algorithms Section 3.4 Tanenbaum s book Kartik Gopalan OS Involvement with Page Table Management Four times when OS deals with page-tables 1. Process creation create page table

More information

Chapter 8 Main Memory

Chapter 8 Main Memory Chapter 8 Main Memory 8.1, 8.2, 8.3, 8.4, 8.5 Chapter 9 Virtual memory 9.1, 9.2, 9.3 https://www.akkadia.org/drepper/cpumemory.pdf Images from Silberschatz Pacific University 1 How does the OS manage memory?

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 Memory Management Background Logical/Virtual Address Space vs Physical Address Space Swapping Contiguous Memory Allocation Segmentation Goals

More information

CHAPTER 8: MEMORY MANAGEMENT. By I-Chen Lin Textbook: Operating System Concepts 9th Ed.

CHAPTER 8: MEMORY MANAGEMENT. By I-Chen Lin Textbook: Operating System Concepts 9th Ed. CHAPTER 8: MEMORY MANAGEMENT By I-Chen Lin Textbook: Operating System Concepts 9th Ed. Chapter 8: Memory Management Background Swapping Contiguous Memory Allocation Segmentation Paging Structure of the

More information

10: Virtual Memory Management

10: Virtual Memory Management CSC400 - Operating Systems 10: Virtual Memory Management J. Sumey Introduction virtual memory management: concerned with the actual management operations of a virtual memory system fetch strategies: when

More information

Virtual Memory - I. Roadmap. Tevfik Koşar. CSE 421/521 - Operating Systems Fall Lecture - XV. University at Buffalo.

Virtual Memory - I. Roadmap. Tevfik Koşar. CSE 421/521 - Operating Systems Fall Lecture - XV. University at Buffalo. CSE /5 - Operating Systems Fall 0 Lecture - XV Virtual Memory - I Tevfik Koşar University at Buffalo October rd, 0 Roadmap Virtual Memory Demand Paging Page Faults Page Replacement Page Replacement Algorithms

More information

UNIT I OVERVIEW OF OPERATING SYSTEMS

UNIT I OVERVIEW OF OPERATING SYSTEMS UNIT I OVERVIEW OF OPERATING SYSTEMS Introduction - overview of operating system concepts - Process management and Scheduling, Memory management: partitioning, paging, segmentation, virtual memory, Device

More information