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Memory Management What if pgm mem > main mem ?

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Page 1: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Memory Management

What if pgm mem > main mem ?

Page 2: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Memory Management

What if pgm mem > main mem ?

Overlays – program controlled

Page 3: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Memory Management

What if pgm mem > main mem ?

Virtual Memory – OS controlled (with architecture help)

Page 4: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Memory Management

Separate physical, logical address space

Page faults

Demand paging

Page 5: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Memory Access in VM

Is access legal ? (seg fault) If page in physical memory, return mem Else

Find free page Schedule disk operation Perform disk operation Update page table Restart program at offending address

Page 6: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Memory Access Time

Assume machine characteristics 200ns clock rate Main Mem access of 5 cycles 1000ns 25 milisecond page service time

Page 7: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Computing Average Access Time

MAT = (1 – p) * 1000 + p * 25,000,000

e.g. assume page fault rate of .001

MAT = .999 * 1000 + .001 * 25,000,000 = 999 + 25,000 26x penalty

Page 8: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Your Turn

Those were 1998 numbers Assume 2x speedup in clock speed every two

years, 2x speedup in disk access time every 4 years

What penalty would .001 page fault rate lead to in 2010?

What page fault rate would allow MAT of 2x main memory access time.

Page 9: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Replacement Policy (Page)

FIFO Random Optimal LRU LRU approximation

Page 10: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Sample References

7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1

Page 11: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

FIFO – 4 pages

7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1

2

1 4

3 72104

2 0 1 2

1 20

3

3 4 0 1

7 0 1 2 3 4 0

Page 12: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Optimal – 4 pages

7 0 1 2 0 3 0 4 2 3 0 3 2 1 0 1 7 0 1

2

1 4

2 112

1 7

0 00

4

0 0

7 3 3 3 3

Page 13: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

LRU – 4 pages

7 0 1 2 0 3 0 4 2 3 0 3 2 1 0 1 7 0 1

2

1 1

2 222

1 1

0 00

4

0 0

7 3 3 3 7

Page 14: Memory Management What if pgm mem > main mem ?. Memory Management What if pgm mem > main mem ? Overlays – program controlled

Your Turn

7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1

Show FIFO, LRU, Optimal for references above but with 3 pages.