Re: [Xen-devel] [PATCH] Fix domheap structure allocation when NUMA=on

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 20.03.09 09:56 >>>
>On 20/03/2009 08:47, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> virt_to_mfn(DIRECTMAP_VIRT_END - 1) is equal to
>> 
>> Depending on whether DIRECTMAP_VIRT_END is the last byte or the first
>> following byte. Using "- 1" avoids such a dependency.
>> 
>>> virt_to_mfn(DIRECTMAP_VIRT_END - PAGE_SIZE). Why +1? We use '<=' here.
>> 
>> Because on the left side of the comparison we also calculate the first
>> following mfn, not the last included one.
>
>Since DIRECTMAP_VIRT_END is always the following byte not the last byte, it
>sounds like you think the page_alloc.c chunk is not needed at all. I'll just
>check in the header fix for now.

No, that chunk is necessary afaics - as I said I agree to Xiaowei's diagnosis
that virt_to_mfn() should not be used on DIRECTMAP_VIRT_END alone.
Subtracting 1 from it, and then adding back 1 to the result is indeed what
I think is the right thing to do here.

Jan


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