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Date: Mon, 12 Aug 2013 16:25:29 -0500
From: Nathan Fontenot <nfont@linux.vnet.ibm.com>
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 2/2] Register bootmem pages at boot on powerpc
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On 08/12/2013 04:13 PM, Benjamin Herrenschmidt wrote:
> On Mon, 2013-08-12 at 08:01 -0500, Nathan Fontenot wrote:
>>> Can you tell me a bit more, the above makes me nervous...
>>
>> Ok, I agree. that message isn't quite right.
>>
>> What I wanted to convey is that memory hotplug is not fully supported
>> on powerpc with SPARSE_VMEMMAP enabled.. Perhaps the message should read
>> "Memory hotplug is not fully supported for bootmem info nodes".
>>
>> Thoughts?
> 
> Since SPARSE_VMEMMAP is our default and enabled in our distros, that mean
> that memory hotplug isn't fully supported for us in general ?

Actually... We have had the distros (at least SLES 11 and RHEL 6 releases)
disable SPARSE_VMEMMAP in their releases.

> 
> What do you mean by "not fully supported" ? What precisely is missing ?
> What will happen if one tries to plug or unplug memory?

I don't know everything that is missing, but there are several routines
that need to be defined for power to support memory hotplug with SPARSE_VMEMMAP.

> 
> Shouldn't we fix it ?

Working on it, but it's not there yet.

> 
> Cheers,
> Ben.
> 
>