Re: PAE code ?

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On Tue, 11 Oct 2011 06:28:31 +0200, Michael C. Vergallen wrote:
> Strange that the option is available in the 5.1 kernel source-code. I
> will try to re-build the kernel today and see if it works or not
> because I've come to the constatation that  the i386 5.1 daily build
> with the latest  security patches had some problems with the code 
> base
> that seemed odd to me. so I went back to the standard 5.1 build and
> compiled from source like the SA reports indicated.

It's in there for the Xen 3.3+ dom0/domUs, as Xen dropped !PAE support 
i386 starting with 3.3. You shouldn't have the PAE options available in 
GENERIC config(5) file, even commented out.

Don't try compiling it, and even if it does there's no chance that it 
will ever work on the machine, except maybe for UP system (which does 
not seem to be the case for yours). The original (-5) PAE code used a 
static L3 page for PAE mappings (Xen domains being UP back then), 
porting it to GENERIC required to drop it in favor of per-CPU allocated 
L3 pages. This changes quite a few things in the pmap and context switch 
code, and these are critical parts of a kernel you don't modify unless 
you really need too :)

> > What memory are you talking about? The memory resource is managed at 
> > system level, pinning memory to a CPU would be a waste of resource as 
> > you cannot tell in advance where it will be required. No decent modern 
> > OS should do that, except for very specific reasons like NUMA (and 
> > even there, it's more a matter of locality rather than allocation).
> I was just thinking out loud on this issue and just wordered if it
> was possible. You are right I didn't consider the memory management
> issues. Also I might got things confused by thinking this is what XEN
> does ... I've got no experience with system virtualisation outside of
> playing with opensolaris zones and that is a while back.

If you really need PAE, give a -current GENERIC kernel a try without 
touching the userland. Binary compat for -5 should take care of 
everything without much hassle. Once NetBSD-6 is branched, update the 
entire system.

Yes, this isn't perfect, but that's the only way I can think of if you 
need PAE. Or use amd64, you can run 32 bits binaries on a NetBSD 64 bits 
box.

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost