Removing kernel thread stack swapping

[Stephan Uphoff]

On Tue, 2005-03-15 at 20:43, Peter Wemm wrote:
> On Thursday 03 March 2005 07:35 am, David Schultz wrote:
> > On Thu, Mar 03, 2005, John Baldwin wrote:
> [..]
> > > Hence, don't kill this whole feature just because someone is too
> > > lazy to fix a bug.
> >
> > Fair enough.  I'll defer to you on the extent of the problem.
> > David seemed to think that it was more widespread.  (BTW, does
> > *anyone* know what the PHOLD() in kern_physio is for?  Is it a
> > holdover from when the PCB was in struct user?)
> 
> I've wondered about this myself in the past.  I went looking once and 
> discovered that it never did anything that I could find.  I believe it 
> is a case of 'because it was always done that way' or because the 
> pseudocode in the Bach or bsd books had it.  There is certainly no 
> functional need for it in FreeBSD.

kern_physio prevents chunks of memory needed for IO from being paged
out. Swapping out a thread in kern_physio will prevent it from releasing
the resources soon. With minphys > stack size I think PHOLD() is still a
good idea.

Stephan