Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!leah!rpi!rpi.edu!deven
From: deven@rpi.edu (Deven Corzine)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Virtual Memory / doable 1.4 request
Message-ID: <DEVEN.89May18030522@daniel.rpi.edu>
Date: 18 May 89 07:05:22 GMT
References: <8905132040.AA27524@postgres.Berkeley.EDU> <DEVEN.89May17023146@daniel.rpi.edu> <347@mohawk.cs.utexas.edu>
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In-reply-to: bryan@cs.utexas.edu's message of 17 May 89 21:50:05 GMT

In article <347@mohawk.cs.utexas.edu> bryan@cs.utexas.edu (Bryan Bayerdorffer @ Wit's End) writes:

>       Yeah, I thought of posting the same response to Matt's
>article, but there is a problem.  Neglecting chip RAM, the reason a
>task needs physical memory is to guarantee fixed execution time for
>instructions, and for calls to AllocMem.  Now, you can lock the page
>frames occupied by the code at load time, but if you allow AllocMem
>to kick out a VM page, and the page is dirty, then you have to wait
>for the pager to run and write the page out to disk.  I can think of
>a couple of solutions to this, but none are much better than
>statically partitioning memory.  Of course, if you don't run any
>real-time programs, then the idea remains elegant, and I'm glad I had
>it first. :-)

Thpppt.  I had it first. :-)

Seriously, you could help that situation by reserving a set amount of
free real RAM that should be available at any given time.  It could
act as a buffer so the pager could free more pages while the program
merrily goes and uses the memory it allocated.  Alternatively, (or
conjunctively, or something) you could have a maximum number of
"dirty" pages the pager may have...  and allow it to use as much
memory as is available for read-only pages, which can be (almost)
instantly flushed.  Basically, this comes down to minimum clean free
pages, but without necessarily wasting them...

That's the idea, anyhow.

Deven
--
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