Question

There are four processes A(36 pages), B(20 pages) C(28 pages) and D(96 pages) that are requesting free frames to be allocated to them out of a total of 92 frames. How many frames would the processes be allocated with a) fixed allocation b) proportional allocation?

Answer 1

Allocation of Page Frames

• Several physical pages allocated to processes A, B, and C. Process B page faults
• Each process needs minimum number of pages
• Want to make sure that all processes that are loaded into memory can make forward progress
• Example: IBM 370 – 6 pages to handle SS MOVE instruction:

 instruction is 6 bytes, might span 2 pages

 2 pages to handle from

 2 pages to handle to

Fixed Allocation

• Allocate a minimum number of frames per process

Consider minimum requirements, e.g. on previous slide

 One page from the current executed instruction

 Most instructions require two operands

 Include an extra page for paging out and one for paging in

Proportional Allocation

• Allocate a number of frames per job proportional to job size

Priority Allocation

 May want to give high priority process more memory than low priority process

 Use a proportional allocation scheme using priorities instead of size