40 vs 44 bit memory addressing HP DL580/980
Alan Cox
alc at rice.edu
Tue Nov 23 01:01:51 UTC 2010
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.
Alan
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