Re: [Bugme-new] [Bug 2019] New: Bug from the mm subsystem involving X (fwd)

[Martin J. Bligh]

>> which seems to be the "PageReserved(pfn_to_page(pfn))" test.
>> 
>> This implies that you have either:
>>  - a buggy "pfn_valid()" macro (do you use CONFIG_DISCONTIGMEM?)
> 
> Yup.
># define pfn_valid(pfn)          ((pfn) < num_physpages)
> 
> Which is wrong. There's a even a comment above it that says:
> 
> /*
>  * pfn_valid should be made as fast as possible, and the current definition
>  * is valid for machines that are NUMA, but still contiguous, which is what
>  * is currently supported. A more generalised, but slower definition would
>  * be something like this - mbligh:
>  * ( pfn_to_pgdat(pfn) && ((pfn) < node_end_pfn(pfn_to_nid(pfn))) )
>  */
> 
> ;-)
> 
> Which I still don't think is correct, as there's a hole in the middle of
> node 0 ... I'll make a new patch up somehow and give to Keith to test ;-)

Oh hell ... I remember what's wrong with this whole bit. pfn_valid is
used inconsistently in different places, IIRC. Linus / Andrew ... what
do you actually want it to mean? Some things seem to use it to say
"the memory here is valid accessible RAM", some things "there is a 
valid struct page for this pfn". I was aiming for the latter, but a
few other arches seemed to disagree.

Could I get a ruling on this? ;-)

Thanks,

M.

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