CS 3733 Operating Systems
Lecture 18 [2/23/98]: Allocation of Frames
Read SG section 9.6
How many frames of real memory should be allocated to process?
- Local allocation
- Global allocation
How many frames?
Let m be the number of frames and n is the number
of processes.
- Equal allocation - give each process m/n.
- Proportional allocation - let si be the
size of virtual memory for process pi. Let
S be the total virtual memory for all processes.
Allocate process i si / S.
- Allocate based on priority.
Trashing occurs when there is not enough real memory
to hold the pages that the processes need. It is characterized
by a catastrophic drop in performance as memory access time
degenerates to disk access time.
Locality Model
Working Set Model
Page-Fault Frequency Strategy
Other Considerations
- Prepaging
- Clustering
- Page size tradeoffs
- Inverted page tables.
Skill: understand the working set model
Revision Date: 2/21/98