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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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