Re: fixing sparc64 pmap_remove_all

[Andrew Doran <ad%NetBSD.org@localhost>]

On Mon, Jan 07, 2008 at 09:53:34PM +0100, Martin Husemann wrote:

> On Mon, Jan 07, 2008 at 09:15:55PM +0100, Tobias Nygren wrote:
> > The problem is that the pmap refcount is set to zero in
> > pmap_remove_all(). No other ports I checked do this.

Nice catch.
 
> pmap_remove_all() is an optimization to avoid a lot of work updating
> mapping only to throw them all away later. So when we know the pmap
> is going away (process exiting), pmap_remove_all() invalidated the
> context, and any further pmap_remove()/pmap_page_protect()/pmap_update()
> calls will avoid heavy work.
> 
> > A working solution is to cast the return value from atomic_dec_uint_nv
> > in pmap_destroy into a signed value. This restores the previous
> > (broken) behaviour. Maybe you guys have a better idea? :-)
> 
> Since pm_refs is an int I think this is the correct solution and the
> previous behaviour is not broken at all. Andrew, what do you think?

pmap_remove_all() will only be called by the last LWP in a process
so the refcount trick is fine, casting the return to (int) seems the
best thing to do. I will make the change shortly.

Thanks,
Andrew