Some ideas for FreeBSD

millueradfa at millueradfa at
Fri Feb 8 17:16:54 UTC 2008

--- "Jason C. Wells" <jcw at> wrote:

> Heiko Wundram (Beenic) wrote:
> > Am Donnerstag, 7. Februar 2008 07:32:16 schrieb
> Jason C. Wells:
> >> Norberto Meijome wrote:
> >>> But I agree with you really want to
> use swap files?
> >> One could mount an md filesystem and then use
> that as swap.  That way
> >> you wouldn't need to use any disc space.  As a
> plus, the performance
> >> would be way better than disc.
> > 
> > Ahem, sorry, that's just plain stupid. Either the
> md system is backed up by 
> > RAM (in which case you don't need the swap anyway;
> why'd you want to access 
> > RAM by putting it in a swap on an md in RAM?), or
> it's backed up by swap, in 
> > which case you have a chicken and egg problem.
> Mmm, yes. That is quite a pickle.  But a chicken or
> an egg would still 
> be inferior to an md backed swap. :)
> Regards,
> Jason
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Actually, you can have file backed swap files. I have
done it. However, with more than one swap file, or a
swap file and a swap partition on the same disk, there
ends up being quite a bit of thrashing. This is due
apparently to some interaction between having two
swaps on the same disk but that is jut a guess, i dont
know what the cause is. 

The idea behind having swap files is that swap space
can more easily be expanded and added on the fly. If
your initial swap partition was not big enough it is
more easy to more swap in another file. As well, a
swap file that can grow and shrink, also would allow
you to avoid having a lot of disk space consumed by
unused swap, so he disk space is allocated when
needed, or allow more space to easily be added if you
find out you do not have enough. 

With applications crashing because of swap partition
running out, this would be an important feature, since
more swap space can be allocated in a file which is
easier to do than a partition.

Swap is still important on systems with small amounts
of RAM, FreeBSD should be able to run on some older
hardware too and should not be like Windows where you
have to have 2 GHZ 2 GB of ram to run it. dynamic swap
space makes it more versatile which is a good thing

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