RE: [Xen-devel] Problem with nr_nodes on large memory NUMA machine

["Subrahmanian, Raj" <raj.subrahmanian@xxxxxxxxxx>]

Beth,
We saw this issue on our boxes too. 
http://lists.xensource.com/archives/html/xen-devel/2007-08/msg00479.html
I am trying to figure out how to write the copy-to-low-memory path. 
Keir, could you give me some suggestions?
Thanks
Raj
>32-bit guests on 64-bit hypervisor can only address the bottom 
>166GB of the memory map, due to constraints on how much of the 
>machine-to-phys array they can reasonably map into their 
>limited address space.
>
> -- Keir
>
>On 19/10/07 16:02, "beth kon" <eak@xxxxxxxxxx> wrote:
>
>> We've run into an issue with an 8 node x3950 where xm info 
>is showing 
>> only 6 nodes. I've traced the problem to the clip_to_limit 
>function in 
>> arch/x86/e820.c.
>> 
>> #ifdef __x86_64__
>>    clip_to_limit((uint64_t)(MACH2PHYS_COMPAT_VIRT_END -
>>                             __HYPERVISOR_COMPAT_VIRT_START) << 10,
>>                  "Only the first %u GB of the physical memory map "
>>                  "can be accessed by 32-on-64 guests."); #endif
>> 
>> Boot messages....
>> (XEN) WARNING: Only the first 166 GB of the physical memory 
>map can be 
>> accessed by 32-on-64 guests. (XEN) Truncating memory map to 
>> 174063616kB
>> 
>> After the memory is clipped, acpi_scan_nodes runs cutoff_node, which 
>> limits the memory associated with each node according to the cutoff 
>> values. Then, acpi_scan_nodes calls unparse_node to "remove" nodes 
>> that don't have the minimum amount of memory, due to the clipping of 
>> the memory range.
>> 
>> Can someone explain what this is all about and why it might 
>be necessary?

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