*BSD News Article 94273


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From: ripley@nostromo.in-berlin.de (H. Eckert)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: How to increase size of vn-device swapfile?
Date: 21 Apr 1997 20:28:07 GMT
Organization: Private access site (FreeBSD 2.2.1), Berlin, Germany, Europe
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aslam@lums.edu.pk (Sohail Aslam):
>   3.  put into /etc/rc.local the line
>            vnconfig -ce /dev/vn0c /var/swap0 swap
> 
> 1. How can increase the size of /var/swap0 (the file)? 

Simply boot into single-user mode so the file isn't in use
as a swap-area.

> 2. How can I disable swapping to the vn-device?

You can't when it has been attached.  This is a design limitation
that presumably can't be removed easily.  To fix this it would be
necessary to designate a swap-area as "dying" so that nothing will
be stored to it anymore.  Every time a page is read from a dying
swap-area it should be transferred to a living one and eventually
nothing is stored in the dying area, so it can be marked dead.  Only
a truly dead area could be detached at all.
Another approach would be to kill all processes that have some pages
in a dying area (not really a good idea) or actively transferring the
pages to a living area (possibly freezing the whole machine in the
meantime).
Anyway, a solution would be quite complicated and would need severe
changes on the heart of the system...

> 3. Is the performance of swapping/paging on a vn-device the same as on
>    a hard partition?

AFAIK direct swapping is more efficient since it doesn't have to
go through the filesystem.

> For the time being, I created another vn-device (vn1c) and another 64MB
> file in /var (swap1) and vnconfig'd swap on it.

Unless you reboot the machine there isn't another way to do it.
Dynamically appending NULs to the active swap-file is something
I'd avoid, too.  I don't think the system would like it.

Greetings,
				Ripley
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