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

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Message-Id: <20160623193739.GA19202@arbab-laptop.austin.ibm.com>
Date:	Thu, 23 Jun 2016 14:37:39 -0500
From:	Reza Arbab <arbab@...ux.vnet.ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Dan Williams <dan.j.williams@...el.com>,
	Balbir Singh <bsingharora@...il.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>,
	Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/mm: update arch_{add,remove}_memory() for radix

On Thu, Jun 23, 2016 at 10:47:20PM +0530, 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 ?

I'm not sure. Maybe it's best if I back up a step and explain what lead 
me to this patch. During hotplug, you get

...
	arch_add_memory
		create_section_mapping
			htab_bolt_mapping
				BUG_ON(!ppc_md.hpte_insert);

So it seemed to me that I needed a radix equivalent of 
create_section_mapping().

After some digging, I found hash__vmemmap_create_mapping() and 
radix__vmemmap_create_mapping() did what I needed. I did not notice the 
#ifdef SPARSEMEM_VMEMMAP around them.

Hotplug/remove are now working for me as far as I can tell, so I think
the functional change in itself was correct. Hotplug may not depend on 
sparsemem vmemmap, but we seem to need a radix create_section_mapping() 
regardless.

Could it be that the functions just need to be renamed 
hash__create_mapping()/radix__create_mapping() and moved out of #ifdef 
SPARSEMEM_VMEMMAP?

-- 
Reza Arbab