Re: UVM crash in NetBSD/i386 PAE with 32 GB of RAM

[David Laight <david%l8s.co.uk@localhost>]

On Tue, Jan 21, 2014 at 08:59:19PM +0100, Christoph Egger wrote:
> Am 21.01.14 20:54, schrieb David Laight:
> > On Tue, Jan 21, 2014 at 10:31:08AM +0000, Emmanuel Dreyfus wrote:
> >> On Mon, Jan 20, 2014 at 04:18:38PM +0000, Emmanuel Dreyfus wrote:
> >>> Changing memory fixed the problem. The machine now boots 6.0 i386 PAE
> >>> with SMP enabled and 128 GB of RAM installed, and it seems to be stable.
> >>
> >> But I spoke too fast. It is stable, but the i386 PAE kernel does not
> >> sees more than 2 GB of memory. An amd64 kernel sees the whole 128 GB.
> >>
> >> Is it possible that the chipset cannot run PAE?
> > 
> > I doubt it.
> > 
> > 2G sounds like the amount of memory below 4G - but I'd have thought that
> > would be 3G (or even 3.5G).
> 
> That depends on the PCI MMIO memory layout.
> 
> And I am wondering if 64bit PCI devices are accessable at all when their
> PCI bar is above 4G.

The bios will put values below 4G into all the bars - otherwise a 32bit
os wouldn't be able to access them at all.
That is why there is a gap in the physical memory addresses.

Actually the size of the memory chips might force 'low' memory
down to 2G - I'm not entirely sure how that memory hole is generated.

If amd64 finds all the memeory, I'd do a bit of chasing through the kernel
startup code to see what happens.

There are KVA issues that might give problems with the page tables
needed for that much physical memory.

        David

-- 
David Laight: david%l8s.co.uk@localhost