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Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!mit-eddie!apollo!hays
From: hays@apollo.UUCP
Newsgroups: comp.os.minix
Subject: Re: File system/virtual memory integration
Message-ID: <335dff58.9540@apollo.uucp>
Date: Fri, 27-Feb-87 13:15:00 EST
Article-I.D.: apollo.335dff58.9540
Posted: Fri Feb 27 13:15:00 1987
Date-Received: Sun, 1-Mar-87 09:35:09 EST
References: <1276@husc6.UUCP> <1057@ius2.cs.cmu.edu>
Reply-To: hays@apollo.UUCP (John Hays)
Organization: Apollo Computer, Chelmsford, MA
Lines: 34
Keywords: file system,virtual memory,Multics

In article <1057@ius2.cs.cmu.edu> ralphw@ius2.cs.cmu.edu (Ralph Hyre) writes:
>I was wondering how difficult it might be to 'integrate' virtual memory
>with the file system process.  I'm told that the Multics operating system
>mapped a file into the virtual address space when it was opened.
>Would this be of any advantages (smaller code size, simpler semantics?)
>in a Minix-based system?

This is also done in Apollo Computer's Domain System and is supported
under it's 3 operating systems BSD4.2/SYS V/AEGIS.

I have used this mechanism to provide some interesting operations on
bitmapped files.

The process need only look at a file as an extension of it's address
space.  It is then possible to do a remapping (ala UNION) between the
file and a data structure (ARRAY or STRUCT) and deal with the file
as data rather than as external storage.

If one combines this capability with a dynamic linking at load, it
is possible to map libraries into global shared memory (which get
paged in VM) and have very small executables greatly reducing link
and load times in the development cycle.  It also makes it possible
for executables to take advantage of updated libraries without
recompilation.

The main problem for implementing this with current MINIX is that
there is (as you know) no support for Virtual Memory in MINIX.


-- 
John D. Hays, Consultant             UUCP: ...!decvax!wanginst!apollo!hays  
Corporate Systems Engineering              ...!uw-beaver!apollo!hays
Apollo Computer Inc.                 CIS: 72725,424  {weekly} 
               !MY OPINIONS, NOT Apollo's!