lightly loaded system eats swap space

Erich Dollansky freebsd.ed.lists at
Tue Jun 19 08:09:25 UTC 2018


On Tue, 19 Jun 2018 09:06:42 +0200
Stefan Esser <se at> wrote:

> Am 19.06.18 um 03:48 schrieb Erich Dollansky:
> > A very long time ago - and not on FreeBSD but maybe on a real BSD -
> > I worked with a system that swapped pages out just to bring it back
> > as one contiguous block. This made a difference those days. I do
> > not know if the code made it out of the university I was working
> > at. I just imagine now that the code made it out and is still in
> > use with the opposite effect.  
> If this was on a VAX, then it was due to a short-coming of the
> MMU of the VAX, which used one linear array (in system virtual

this could have been the case as they have had many DEC systems.

> Nothing of the above applies to any other architecture than the
> VAX and thus the swap-out of all user processes serves no purpose
> on any other system. It was an implementation detail of the VAX
> VM code, not a BSD Unix feature.

I know how an MMU works, but I also know how caches work. It still
could give a tiny advantage if it is in one piece, even if it is not a
requirement to function. Any way, I do not work in this area anymore.


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