*BSD News Article 27721


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From: terry@cs.weber.edu (Terry Lambert)
Newsgroups: comp.os.386bsd.development
Subject: Re: Notes on the *new* FreeBSD V1.1 VM system
Date: 26 Feb 1994 00:43:18 GMT
Organization: Weber State University, Ogden, UT
Lines: 41
Message-ID: <2km5v6$3cb@u.cc.utah.edu>
References: <2khcvv$han@u.cc.utah.edu> <CLqK5I.IzH@ns1.nodak.edu> <wimlCLrCxo.Fvx@netcom.com>
NNTP-Posting-Host: cs.weber.edu

In article <wimlCLrCxo.Fvx@netcom.com> wiml@netcom.com (William Lewis) writes:
>tinguely@plains.NoDak.edu (Mark Tinguely) writes:
>Why can't demand-paged executables act like any other open file? It might
>be a good idea to keep processes from writing to a file that is
>being used as someone's text segment, but is there anything wrong with
>letting them *delete* it? 

[ ... ]

>Of course, there's still the problem with NFS, but this at least makes
>demand-paged executables on local file systems much less annoying.

As you note, there is still the NFS problem to consider...

But actually, doing the copy to swap when ETXTBSY would have been returned
to the user, redoing the operation, and returning to the user as if nothing
had happened was an early fix to the problem.

In the case of the text file overwrite, this solves the problem of how
you MAKE them delete the file before they get to write it -- you don't,
and it doesn't matter.

Of course, this still leaves the other memory overcommit issues unaddressed
and in a similar boat as NFS: ignored, and not resolved.  For instance,
full panic dumps and restart from saved state (power conservation, etc.).

In an exactly analogous case to the NFS server going away, images being
swapped from the program instead of swap will fail if they are loaded
from a pcmcia based adaper that can "go away", and the open instance
for the image will keep FS's from being unmounted for similar reasons;
the swap reference counts as an open.

Overcommit is messy, but has the very appealing trait of letting you
have system memory on credit.  8-).


					Terry Lambert
					terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.