Re: [PATCH] powerpc/mm: update arch_{add,remove}_memory() for radix

[Balbir Singh]

On 24/06/16 03:17, Aneesh Kumar K.V wrote:
> Reza Arbab <arbab@xxxxxxxxxxxxxxxxxx> writes:
> 
>> These functions are making direct calls to the hash table APIs,
>> leading to a BUG() on systems using radix.
>>
>> Switch them to the vmemmap_{create,remove}_mapping() wrappers, and
>> move to the __meminit section.
> 
> 
> They are really not the same. They can possibly end up using different
> base page size. Also vmemmap is available only with SPARSEMEM_VMEMMAP
> enabled. Does hotplug depend on sparsemem vmemmap ?

# eventually, we can have this option just 'select SPARSEMEM'
config MEMORY_HOTPLUG
        bool "Allow for memory hot-add"
        depends on SPARSEMEM || X86_64_ACPI_NUMA
        depends on ARCH_ENABLE_MEMORY_HOTPLUG

We depend on sparsemem for sure. vmemmap is just a way of getting the memory
virtually mapped. From the patch perspective, I think we need the equivalent of
just mapping the pages in kernel. The address may differ based on whether vmemmap
is used or not and of-course page_size, 

Balbir Singh