Layout
Address Memory spaces
x
1
Memory a linear array of bytes
Physical address space that supported by the hardware
y
MAX
starting at address 0, going to address MAX
MAXP
Logical address space a processs view of memory
Program P
y
http://www.cse.unl.edu/~goddard/Courses/CSCE451
starting at address 0, going to address MAXP
0
Memory Management Basics
x
But where do addresses come from?
MOV r0, 0xfffa620e
0
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CSCE 451/851 Operating Systems Principles
2
Steve Goddard
CSCE 451/851 Steve Goddard
Lecture 10
CSCE 451/851 Steve Goddard
Page 2
Lecture 10
Page 1
Address Generation
The compilation pipeline
0 1000
Simple Memory Management Schemes
Fixed-sized partitions
MAX
x
Library Routines Library Routines
1100 : : : jmp 175 : ... : : : jmp 1175 : ...
Two variations:
Jobs queue for partitions
y
Py Px
prog P : : foo() : : end P
P: : push ... inc SP, x jmp _foo : foo: ...
0 : push ... inc SP, x jmp 75 : ...
100
addressing done by the linker/loader
Jobs queue for memory
y
P3 P2 P1
dynamic relocation required
Program P
75
175
1175
x
Scheduling
maximize performance maximize memory utilization Pa 0
Compilation
Assembly
Linking
Loading
3
4
CSCE 451/851 Steve Goddard
Lecture 10
Page 3
CSCE 451/851 Steve Goddard
Lecture 10
Page 4
Dynamic Program Relocation
Program compilation
x
Dynamic Program Relocation
Base + Limit registers
MAX
MEMORY EXCEPTION Logical Addresses
Code relocated at run-time
P: : push ... inc SP, x jmp _foo : foo: ... 0 : push ... SP, inc x jmp 75 : ...
0
1000
Library Routines
prog P : : foo() : : end P 100 : : : jmp 175 : ... 1100
Library Routines
: : : jmp 175 : ...
n
CPU
500
y
+
1000
Physical Addresses
1500
Program Ps PAS
1000
75
175
1175
MAX
Compilation
Assembly
Linking
Loading
(No relocation) 0
Program Ps LAS
Limit Register
Base Register
0
6
5
CSCE 451/851 Steve Goddard
Lecture 10
Page 5
CSCE 451/851 Steve Goddard
Lecture 10
Page 6
Memory Management Issues
Fragmentation
MAX
x
Simple Memory Management Schemes
Variable-sized partitions
x
Internal fragmentation
Program Qs PAS
x
Allocate a partition when a process is admitted into the system Keep track of...
full-blocks empty-blocks (holes)
MAX Program P1
P
x
P5
Program P2
External fragmentation
x
Allocation strategies
first-fit best-fit worst-fit 0
Program P3 Program P4
8
Program 0 Rs PAS
7
CSCE 451/851 Steve Goddard
Lecture 10
Pa...