[PATCH v2] powerpc/pseries: Fix maximum memory value

Michael Ellerman mpe at ellerman.id.au
Thu Jul 4 21:13:26 AEST 2019

"Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> writes:
> Nathan Lynch wrote:
>> Aravinda Prasad <aravinda at linux.vnet.ibm.com> writes:
>>> Calculating the maximum memory based on the number of lmbs
>>> and lmb size does not account for the RMA region. Hence
>>> use memory_hotplug_max(), which already accounts for the
>>> RMA region, to fetch the maximum memory value. Thanks to
>>> Nathan Lynch for suggesting the memory_hotplug_max()
>>> function.
>> Well, I hope I haven't led you astray... will it give you the desired
>> result on a kernel configured without memory hotplug support, booted in
>> an LPAR with some huge pages configured?
>> If so, then
>> Acked-by: Nathan Lynch <nathanl at linux.ibm.com>
>> It would likely help with review and future maintenance if the semantics
>> and intended use of the MaxMem field are made a little more
>> explicit. For example, is it supposed to include persistent memory?
>> Perhaps a follow-up patch could address this. Or maybe I'm overthinking
>> it.
> This was primarily aimed to replicate what AIX lparstat does and 
> documentation (*) just says:
>   Maximum Memory
>       Maximum possible amount of Memory.
> I think this mirrors the maximum memory value set in the LPAR profile, 
> and this provides a way to obtain that value from within the LPAR.

But the doc string for memory_hotplug_max() says:

 * memory_hotplug_max - return max address of memory that may be added

ie. maximum *address* not maximum *amount*.

Possibly it turns out to be the same value, but that is just because you
have no holes in your layout.

So I don't think this patch is correct.


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