Re: HP-PA and MPE XL page architecture

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Article #22664

#22664

From: Andy Glew
Date: Wed, 28 Feb 1990 03:42

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>We spent a long time arguing out what the correct semantics of copy-on-write
>file mapping should be to support transactions, for example if two processes
>map a file COW, should they get the same COW segment or separate ones.  (The
>answer, surprisingly, turns out to be that they get the same one.)  The
>semantics are non-trivial, to the extent that IBM patented the way it works,
>no. 4,742,450.

Copy-on-write filesystems are certainly useful. Dave Yost's "Rich Person's
Configuration Control System" (USENIX Summer 1985) is basically COW on
file granularity (I carried the same idea forward).  Finer granularity
would be nice.  SCCS/RCS, if you look at them the right way, are COW files.

All the arguments for file mapping apply to mapping of COW files.
--
Andy Glew, aglew@uiuc.edu

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From: aglew@dwarfs.csg.uiuc.edu (Andy Glew)
Newsgroups: comp.arch
Subject: Re: HP-PA and MPE XL page architecture
Message-ID: <AGLEW.90Feb27214254@dwarfs.csg.uiuc.edu>
Date: 28 Feb 90 03:42:54 GMT
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In-Reply-To: johnl@esegue.segue.boston.ma.us's message of 27 Feb 90 02:48:18 GMT

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