Re: 40 vs 44 bit memory addressing HP DL580/980

On Monday, November 22, 2010 8:01:34 pm Alan Cox wrote:
> On 11/22/2010 1:47 PM, John Baldwin wrote:
> > On Monday, November 22, 2010 1:37:45 pm Alan Cox wrote:
> >> On Mon, Nov 22, 2010 at 6:59 AM, John Baldwin<jhb_at_freebsd.org>  wrote:
> >>
> >>> On Sunday, November 21, 2010 8:05:26 pm Sean Bruno wrote:
> >>>> Looks like these HP boxes have the capability to do 44 bit memory
> >>>> addressing if configured to do so from the BIOS.
> >>>>
> >>>> Is anyone interested in any data from that setting?
> >>> Does it boot ok? :)  The MTRR code should handle that (there is a CPUID
> >>> field that tells the OS how many bits are significant).  Not sure if there
> >>> are any places in the pmap that assume 40 bits, but a test boot is
> >>> certainly
> >>> worth trying.
> >>>
> >>>
> >> Since we don't boot with 40-bit addressing, I can easily predict the
> >> outcome.  :-)
> >>
> >> The trouble with this machine is that the second 128GB of RAM is being
> >> placed between 512G and 1T in the physical address space, which is beyond
> >> the range of the (current) direct map.  So, we take a page fault on the
> >> first access to a page in the second 128GB through the direct map.
> > Heh, I guess that is what your earlier patch did?  Once that patch is applied
> > I think Sean should just try 44-bit mode if so.
> >
> 
> Yes.
> 
> If 44-bit addressing makes the placement of DRAM in the physical address 
> space any sparser, then we'll again have an insufficiently large direct 
> map.  Also, I fear that we won't be able to allocate the vm_page_array 
> without enabling VM_PHYSSEG_SPARSE, which itself requires a change in 
> order to work.

I believe someone has a change for that on amd64 already?

-- 
John Baldwin