Path: utzoo!attcan!uunet!mcvax!enea!kth!draken!tut!santra!kampi!jmunkki
From: jmunkki@kampi.hut.fi (Juri Munkki)
Newsgroups: comp.sys.mac
Subject: Re: Virtual memory init
Message-ID: <18721@santra.UUCP>
Date: 16 Jan 89 00:21:26 GMT
References: <1542@csuna.UUCP> <7124@netnews.upenn.edu> <13566@cup.portal.com>
Sender: news@santra.UUCP
Reply-To: jmunkki@kampi.UUCP (Juri Munkki)
Organization: Helsinki University of Technology, Finland
Lines: 30

In article <13566@cup.portal.com> ts@cup.portal.com (Tim W Smith) writes:
>What happens if I get a page fault in the middle of a SCSI operation?
>For instance, suppose my code does this:
>
>	SCSIGet();
>	SCSISelect( id );
>	SCSICmd( cmdBuf, 6 );
>
>and the memory pointed to by cmdBuf has been paged out.  How does the
>init manage to read that page off the disk?

Good question! I haven't seen the product and all I know about is what
has been written about it on Comp.sys.mac, but I guess they could have
patched FSRead and FSWrite so that the calls make sure that they are
operating on available pages. A really long read or write would then
have to be split into several smaller segments so that 1 or 2 megabytes
of RAM would be enough.

Along the same lines: how do they know which parts of the system heap
they can swap out. I thought about writing a virtual memory INIT, but
I couldn't think of a way to let it swap out parts of the system heap.

We're definitely going to try the product at our university. I might
even get one myself, if I can't get a NeXT this year. They should
sell it for $150...I think they'd make a lot more money that way...

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|     Juri Munkki jmunkki@hut.fi  jmunkki@fingate.bitnet        I Want   Ne   |
|     Helsinki University of Technology Computing Centre        My Own   XT   |
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