Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rochester!ur-tut!tuba
From: tuba@ur-tut.UUCP (Jon Krueger)
Newsgroups: net.arch
Subject: Re: VERY LARGE main memories
Message-ID: <676@ur-tut.UUCP>
Date: Thu, 11-Sep-86 13:44:31 EDT
Article-I.D.: ur-tut.676
Posted: Thu Sep 11 13:44:31 1986
Date-Received: Fri, 12-Sep-86 22:15:19 EDT
References: <1130@bu-cs.bu-cs.BU.EDU> <7144@lanl.ARPA> <7148@lanl.ARPA> <7094@utzoo.UUCP> <7331@lanl.ARPA>
Reply-To: tuba@ur-tut.UUCP (Jon Krueger)
Organization: Univ. of Rochester Computing Center
Lines: 38
Keywords: VM economy tradeoff


In article <7331@lanl.ARPA> jlg@a.UUCP (Jim Giles) writes:
>It's not just that the operating system or hardware designers are too lazy
>to come up with a good scheme.  The problem is that any scheme they DO come
>up with must work for general cases.  That is, it can't take advantage of
>special knowledge of a specific algorithm....The individual applications
>programmer CAN take advantage of such knowledge.  To be sure, this is an
>expensive and difficult programming project...[but] there are some types of
>algorithm for which it is extremely easy to predict the data usage
>patterns.  Now, it might be convenient to implement virtual memory schemes
>which are useful in this context, but I doubt that the extra overhead in the
>memory interface would be justified - especially since the explicit methods
>for dealing with them are fairly easy to implement.

1) Doubtless you can show me cases where it's "extremely easy" to predict
data usage patterns.  Can you show me one where it's easy to predict the
code usage patterns?  I want VM to free me from overlays, or code space
management, not file structuring, or data space management.

>if you've just spent $10-$20 million on a fast machine, you aren't going
>to balk at a few million more in programmer man-hours to get the speed
>that you shelled out so much cash for.
2) Can we measure the win?  Can you provide figures on performance
improvements for either data or code space management by application
programmers over mechanisms provided by operating system or hardware
designers?  Have you any actual examples, how much was the improvement for a
specific application you're familiar with?  Can we state a general rule,
expected returns on applications programmers managing their own code and/or
data spaces?  Can you state the breakeven point, how many millions of
dollars I should be willing to spend before I improve on the operating
system's paging?

					-- jon
-- 
--> Jon Krueger
uucp: {seismo, allegra, decvax, cmcl2, topaz, harvard}!rochester!ur-tut!tuba
Phone: (716) 275-2811 work, 473-4124 home	BITNET: TUBA@UORDBV
USMAIL:  Taylor Hall, University of Rochester, Rochester NY  14627