Chapter 9 Virtual Memory
Programs larger than physical memory
Abstract memory into a large, uniform array
Virtual memory, virtual address space vs. physical memory, physical address space
Pages -- sized to power of 2
Benefits/Needs p316
Demand paging, Pure demand paging
Lazy pager, valid-invalid bit, page table
Page-fault trap p321
Locality of Reference
Effective access time, calculation
Copy-on-write
Page-replacement Algorithms vs. Frame-allocation Algorithms
Dirty bit, victim frame, reference string
FIFO, Belady's Anomaly
Optimal -- lowest page-fault rate, never suffer from Belady's Anomaly
LRU & approximations
Second-Chance Algorithm
Page-Buffering -- pool of free frames, write-out when idle
Raw disk I/O
Allocation of Frames
Minimum number of frames
Equal, proportional, priority allocation schemes
Global vs. local allocation
Thrashing
Increases in multiprogramming as a cause
Typical profile -- fig 9.18, p344
Locality model
Working-Set Model -- working set, window, page-fault frequency (PFF)
Memory-Mapped Files
Allocation of memory
Other considerations
Page Size p357
Small pages better
memory utilization, smaller transfer time, better resolution/locality
Large pages smaller page table, total I/O time, minimize page faults, larger TLB reach
Inverted page tables