*BSD News Article 69977


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From: root@dyson.iquest.net (John S. Dyson)
Subject: Re: MFS - Why?
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References: <AEn4jRr0u3@qsar.chem.msu.su> <npX7tgO@quack.kfu.com> <833457338.26209.0@arg1.demon.co.uk> <nqcignn@quack.kfu.com>
Date: Sun, 2 Jun 1996 06:15:23 GMT
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In article <nqcignn@quack.kfu.com>, Nick Sayer <nsayer@quack.kfu.com> wrote:
>
>>You can use the vnode driver (see vnconfig(8)) to allow swapping into a
>>regular file.  It may not be quite as convenient as some other OSs,
>>but it certainly solves the problem.
>
>How? Once you add a swap area you can't remove it. So you can't
>prepare for a large job by adding temporary extra swap, do the work
>and then remove and dispose of this extra swap. That would be the
>only equivalent behavior. Solaris 2.x can do this, but FreeBSD can't.
>And in any case this behavior is not automatic.
>
That is a significant limitation that Jordan has wanted for quite a while.
After we settle down from the latest VM megacommit (super-fast fork times,
and vastly improved exec times), I am going to do the swapon/swapoff thing
correctly.  The swapon of a vnode is pretty simple, but swapoff will require
verification that there is enough swap space after the partition is removed,
and paging-in/out of the data that resides on the old partition.  No
biggie, just will take a bit of time.  It is really odd that this subject
would come up again, just when I plan to implement it :-).

>
>Don't get me wrong -- I still prefer FreeBSD to the alternatives,
>but not being able to 'swapoff' is a bit of a bummer.
>
Thanks for the vote of confidence :-)!!!

John
dyson@freebsd.org