From: Ankur Rawat \(Excell Data Corporation\) (a-arawat_at_microsoft.com)
Date: Wed Feb 11 2004 - 15:53:22 PST
This paper talks about the implementation of Virtual memory management
system in VAX/VMS OS.
The VMM system is divided into 2 parts:
* Process space
* System space
The Process space is again divided into 2 regions P0 and P1. I liked the
idea of having 2 registers for each region's page table. I think not
storing page table references in memory prevents a substantial disk I/O
overhead. Dividing the use translation buffer into parts also avoids
computational overhead.
The protection mechanisms provided by the VMM system were not very clear
to me particularly in the light of - system space being mapped into
every user process. The system designers try to address the concern of a
paging process impact on others by using a process-local page
replacement policy. They try to address the increased workload concern
by using clustering of pages. The system delays paging out to disk using
modify lists and free lists.
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