U Area Removal

[David Schultz]

On Thu, Nov 11, 2004, Scott Long wrote:
> >I propose to remove the ability to swap the U area, allocating p_stats
> >from malloced memory instead.  Medium-term scheduling and swapping of
> >kernel stacks would be retained.  Here are the patches; !i386 testers
> >wanted:
> >
> >	http://www.freebsd.org/~das/patches/upages.diff
> >
> >
> >[1] Most of the instances of PHOLD() and PRELE() right now never
> >    needed to be there or have been unnecessary ever since the PCB
> >    was moved out of the U area.
> 
> 
> This breaks amd64 in bad ways on boot.  I'll send a trace and more info
> when I get a serial console hooked up.

The bug jhb mentioned may be responsible for this:

| +struct pstats *
| +pstats_alloc(void)
| +{
| +
| +       return (malloc(sizeof(struct plimit), M_SUBPROC, M_ZERO|M_WAITOK));
| +}
| 
| I think you mean s/plimit/pstats/ there.

On 32-bit architectures, sizeof(struct plimit) is 184 bytes and
sizeof(struct pstats) is 216 bytes, so requests for either would
get a 256-byte allocation and things work fine.  But on 64-bit
architectures, sizeof(struct plimit) is 192 bytes and
sizeof(struct pstats) is 432 bytes...

In any case, I've updated the patch to correct this cut-and-paste-o.