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From: ttwang@polyslo.CalPoly.EDU (Thomas Wang)
Newsgroups: comp.arch,comp.sys.mips
Subject: Re: Memory utilization & inter-process contention
Message-ID: <13773@polyslo.CalPoly.EDU>
Date: 25 Aug 89 00:37:18 GMT
References: <3332@blake.acs.washington.edu>
Reply-To: ttwang@polyslo.CalPoly.EDU (Thomas Wang)
Distribution: usa
Organization: Cal Poly State University -- San Luis Obispo
Lines: 24

lgy@newton.phys.washington.edu (Laurence Yaffe) writes:

>    A lot of current machines, such as my MIPS box, have pretty standard
>virtual memory systems: demand paging is used to allocate real memory to
>individual processes, with some sort of least-recently-used algorithm
>employed to select pages to write out.
>Severe, and unnecessary, performance degradation can occur if you have several
>processes which have very poor locality of reference when accessing their
>data, are sufficiently small that any singly process can fit in real memory,
>and yet sufficiently large that no two processes will fit in real memory.

To avoid excessive page fault rate, a good algorithm is to load in multiple
pages depending on system load.  Actually how many pages should you load in
is still a research question.  In HP's term, loading in extra pages is
called 'pre-fetching'.

HP's MPE/XL have pre-fetching.  I don't know about Unix, but my guess is
that Unix probably does not.


 -Thomas Wang ("I am, therefore I am."
                 - Akira               )

                                                     ttwang@polyslo.calpoly.edu