Re: [PATCH v5 2/6] xen/x86: move generically usable NUMA code from x86 to common

[Wei Chen <Wei.Chen@arm.com>]

Hi Jan,

On 2022/9/27 17:39, Jan Beulich wrote:
> It's the comment which is wrong - it wasn't updated in Linux commit
> 54413927f022 ("x86-64: x86_64-make-the-numa-hash-function-nodemap-allocation
> fix fix"). Our code was cloned from Linux'es. In fact when memory is not
> contiguous, too small a shift value might be determined. This in particular
> also may matter for the lowest range covered by any node: On x86 this will
> always start at zero (and hence won't influence the final calculation), but
> iirc on Arm memory may (and typically will) start at non-zero addresses. In
> such a case the first node's start address should be ignored, as it's fine
> to (kind of) associate all lower addresses (where no memory is) with this
> same node. But that's now indeed something which will want taking care of
> while making the code usable for other architectures

Sorry, I hadn't read this before my last reply. I think I kind of 
understand what you mean now. If we do not ignore the lowest memory 
start address in the node, then the shift we calculate may contain a 
part of non-ram physical addresses. But if we ignore it, which address 
should we start from? Counting from end may ignore most of the ram area 
on this node.

Cheers,
Wei Chen