linux-kernel - Re: [PATCH] powerpc/mm: update arch_{add,remove}

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Date:	Fri, 24 Jun 2016 13:22:37 +1000
From:	Balbir Singh <bsingharora@...il.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Reza Arbab <arbab@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Dan Williams <dan.j.williams@...el.com>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	David Gibson <david@...son.dropbear.id.au>,
	Vasant Hegde <hegdevasant@...ux.vnet.ibm.com>,
	Scott Wood <scottwood@...escale.com>,
	Oliver O'Halloran <oohall@...il.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/mm: update arch_{add,remove}_memory() for radix



On 24/06/16 03:17, Aneesh Kumar K.V wrote:
> Reza Arbab <arbab@...ux.vnet.ibm.com> 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