Memory Management

Memory Management SunMoon University

Memory or Storage • Real Memory • physical main memory • Virtual Memory • storage conceived by users SunMoon University

Problem of Memory Management(1) • How many jobs in memory at one time • programs or processes • Storage amount per job • same size • different size SunMoon University

Problem of Memory Management(2) • Location to run a job • Fixed  absolute binding and loading • Variable  relocate binding and loading • binding • loading • linking • compiler SunMoon University

주소 번역 j int tiger; int lion; int cat; int dog; main() { L1: tiger++; lion++; goto L1; } main: mov ax, bx mov cx, dx L1: mov ax, tiger add ax mov _tiger, ax mov bx, _lion add bx mov _lion, bx goto L1 end 1011 1110 1111 1011 1110 1000 1110 1000 1110 1101 1000 1111 1101 (D) Text Load Data (A) C source program (C)binary code Stack (B) 가상 assembly program SunMoon University

Instruction Cycle Address … … 104 108 … … C P U Main : … … mov a1, b1 mov a2, b2 … … P C 104 108 I R Mov a1, b1 Mov a2, b2 < Assembly file> SunMoon University

Instruction Cycle j (D) (A) (B) < Memory > SunMoon University

OSvs.Compilervs.Loader u Compiler Loader OS Memory Manager Kernel OS XXXX (C)binary code 적재 (C)binary code (A) C source program (B) assembly program < Memory > < H/D > 적재될 Memory 주소 XXXX가 어느곳인가? SunMoon University

적재할 메모리 주소를 알고 있는 경우 n Compiler Loader (A) (D) Compiler가 OS의 Memory 관리자로부터 메모리에 적재할 주소(ex)1000번지)를 미리 통보 받아 알고 있다. 컴파일러가 직접 메모리상의 주소를 생성 로더는 단순 적재(Absolute loader) SunMoon University < Memory >

적재할 메모리 주소를 모르는 경우1 g Compiler는 가상의 주소(ex) 0번지)에 적재된다고 가정하고 주소 생성 Loader가 적재되는 시점에 OS로부터 가용한 메모리 주소(ex)3500번지)를 통보 받는다. Loader는 새로운 주소로 바꾸고 (Relocatable Loader)적재한다. SunMoon University

적재할 메모리 주소를 모르는 경우2 g 컴파일러는 X(0번지)에서 시작하는것으로 생각하고 주소를 생성한다. 실제 주소는 X에서 3500을 더한다. X main: mov ax, bx mov cx, dx L1: mov ax, tiger add ax mov _tiger, ax mov bx, _lion add bx mov _lion, bx goto L1 end Compiler Loader 새로운 주소로 바꾼다. (A) (D) SunMoon University < Memory >

Problem of Memory Management(3) • Memory Partition Method • Static (fixed) binding • Dynamic(variable) binding • Placement Method for a job • Contiguous • Noncontiguous SunMoon University

Storage Hierarchy • Cache memory • Associative memory • RAM(Random Access Memory) • Hard Disk • etc. • Dfigure 7.1 SunMoon University

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Memory Management Strategies(1) • Obtaining the best possible use of main memory resources 1. Fetch Strategies 2. Placement Strategies 3. Replacement Startegies SunMoon University

Fetch Strategies • Definition : • when to obtain the next piece of program or data to transfer from secondary storage to main memory • Demand Fetch • when it is referenced by a running program • Anticipatory Fetch • improve system performance SunMoon University

Placement Strategies • Definition • where in main memory to place an incoming program • First-fit • Best-fit • Worst-fit SunMoon University

Replacement Strategies • Definition : • which piece of program or data to displace to make room for incoming program • FiFO, LRU, … • vs.) swapping • develop to ‘paging’ or ‘segmentation’ SunMoon University

Storage Allocation • Contiguous Storage Allocation • easy • Noncontiguous Storage Allocation • partition a program into several block or segment • efficient SunMoon University

Single User Allocation(1) • Single user • Dfigure 7.2 • Waste resources • Size of program < size of memory • overlay • main memory 보다 큰 size의 프로그램을 실행시킨다. • Dfigure 7.3 • develop to “Virtual Memory” SunMoon University

Single User Allocation(2) • Protection • protection for OS : no protection in XT, AT • boundary register • whenever program reference the main memory • supervisor call • Dfigure 7.4 SunMoon University

Fixed Partition Multiprogramming(1) • In general, more memory than single user system • CPU utilization on a single user system • better utilization of the CPU • Dfigure 7.5 • Definition : • devide main memory into fixed size partition • each partition has a single job SunMoon University

Fixed Partition Multiprogramming(2) • Absolute loader • Absolute translation and loading • Dfigure 7.6/7.7 • Assign the job to a special partition • Storage waste • Wait a job when the other partition are available • Easy SunMoon University

Fixed Partition Multiprogramming(3) • Relocatable loader • relocatable translation and loading • assign a job to any available partition • Dfigure 7.8 • Protection in multiprogramming • Use several boundary register • Dfigure 7.9 • Fragmentation in fixed partition multiprogramming • Unused space in each partition SunMoon University

Variable Partition Multiprogramming(1) • Minimize fragmentation • No fixed boundary • Contiguous allocation of each job • Partition of each job • Size of partition • No fragmentation in a partition • “hole” • 그림 7.7/7.8/7.10 SunMoon University

Variable Partition Multiprogramming(2) • Solution of fragmentation • Coalescing holes(통합) • borders on other free storage areas • Storage Compaction(집약) • garbage collection • 그림 7.11 / 7.12 • problem • consume system resource(CPU time) • system must stop everything • Interactive , real-time , etc. • relocated once more SunMoon University

Placement Strategies • Dfigure 7.14 • Best-fit • First-fit • Worst-fit SunMoon University

Memory Management