From: Chuck Reeves (creeves_at_windows.microsoft.com)
Date: Wed Feb 11 2004 - 16:56:26 PST
The paper "Virtual Memory Management in VAX/VMS" was written in 1982 by
Henry Levy and Peter Lipman while working as employees for DEC. It
discusses the memory management facilities on the VAX-11. It describes
the decomposition of the a 32-bit address space into 3 primary regions,
System, P1 and P0. The system region is where the OS procedures and code
are located. User programs occupy the P0 space and grow into higher
memory addresses towards the P1 boundary. The user stack occupies the P1
region and grows towards lower memory addresses towards the P0 space.
Page tables are used to manage the state of the pages currently in
memory. The system uses a "pager" object to control which physical pages
of information are loaded into memory. One key optimization made was to
page out memory from processes that requested it when possible. In this
way a poorly behaving application will have minimal impact on other
applications. Other optimizations include caching modified pages to
enable clustering of the pages that are frequently loaded into
consectutive locations in memory. I would appreciate some diagrams
describing the interaction between the page table and the associated
lists to better understand this document. Also the utility of the copy
on reference behavior escaped me.
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