Subject: Re: Virtual Memory Subsystem
To: Niklas Hallqvist <>
From: Zdenek Salvet <>
List: port-i386
Date: 11/26/1996 22:01:50
> > 
> > (Charles M. Hannum) writes:
> > 
> > >Their `fix' will occasionally remove an object that another object is
> > >pointing to, causing stray pointer references.  We were, in fact,
> > >working with Niklas to fix this, but he apparently decided it wasn't
> > >important enough to get it right, and punted.
> > 
> > If I've followed this correctly, the OpenBSD fix:
> > 
> > 	i) collapses shadow-copy object chains by copying
> > 	   swap pages from one object to another, (i.e., involving paging
> > 	   and copying), and
> Well, there are several cases, the most common is actually just renaming
> pages which is cheap.  There is however the "expensive" case which occurs
> very seldom, and that requires pagein alright.  Actually BSD/OS skips this
> case, apparently just the "cheap" collapsing operation suffices for them.

Now I can see why the BSD/OS fix doesn't work in my BSD/OS machines at all.
That case probably is not as rare as you think.

Zdenek Salvet                                     
           If God had meant for us to be in the Army,
         we would have been born with green, baggy skin.