On Sun, 16 May 1999 16:27:25 +0200 
 Manuel Bouyer <bouyer@antioche.eu.org> wrote:

 > Ok. So imagine we support Dynaswap, and you have 10G free on our HD.
 > A user starts such a program, and you want to install emacs. How
 > surprinsing, there's not enouth free space.
 > Second senario: A user ftp'd 10G of MP3 files. You can't start your program
 > any more.

I've been sort of half-following this thread, and it's been giving me a
lot of anxiety :-)

"No, please, the pain has already stopped!"

I remember, before we installed NetBSD 0.9C on the lab's hp300s, running
various versions of HP-UX for the hp300 at the Ore. State CS department.
HP-UX for the 300 didn't have any disk partitioning scheme (unlike HP-UX
for the 800, which supported System V `slices').  So, in order to use
swap space, you had to "swap to the end of the file system" (HP term for
it).

This caused SO much trouble.  On one machine, a 9000/360, which was the mail
hub for the entire research network, the machine often croaked when the mailq
got too large... no more space to swap out an in-core process to fire up
another sendmail process.  It's not like we could just add more disks, either;
we had a limited number of HP-IB 7958s :-)

On the other hand, the undergrad network had a similar machine running
NetBSD _0.9C_.  This machine seldom croaked; there was always enough room
to swap something out, precisely because we didn't have that "swap to the
end of the file system" ... ahem ... feature.

Personally, I like the idea of being able to reserve these kinds of
resources.  Especailly swap space; I mean, if you're using it, you're
already encountering a resource shortage, by definition!  Best that your
fallback mechanism be robust.

And, hey, if you want to swap to some unused file system space on your system,
go for it!  Use "dd" to create a large file, and use swapctl to enable
swapping to it!

        -- Jason R. Thorpe <thorpej@nas.nasa.gov>