Subject: Re: Virtual Memory Subsystem
To: Jukka Marin <>
From: John S. Dyson <>
List: port-i386
Date: 11/26/1996 07:46:48
> > OpenBSD has a fix. It's sub-optimal but perhaps we could use it
> > until a _real_ fix of the VM system is done?
> If it fixes the problem and causes no new ones - I vote YES, please.
> > I don't understand. 
> > 
> > There is a fix for that in -current, and has been, I beleive, since
> > before 1.2 was released. I hope it goes in as an official patch for
> > 1.2.  The relevant change was from 1.23 to 1.24 of
> > sys/vm/vm_pageout.c. pr #2755 explains the problem.
> Sorry.  I was under the impression that there was a "fix" but it caused some
> new problems or didn't fix the problem in all situations.
I looked at the OpenBSD "fix", and was a "solution" that we specifically
decided not to implement on FreeBSD 3yrs ago.  It is better than nothing
though.  It is impossible to fix the problem unless at least a solution
of the type that OpenBSD has implemented is put into place.  I disagree
with the OpenBSD "fix", because it is sub optimal, but is certainly easier
than the complete (and complex) fix that FreeBSD has implemented.

Note that the FreeBSD fix is a virtual (metadata) copy, while the OpenBSD
"fix" is a physical copy.  The physical copy scheme certainly doesn't help
system loading problems under heavy paging conditions.