linux-kernel - Re: x86_64 memory hotplug simulation support?

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Message-Id: <200707051644.55191.nigel@nigel.suspend2.net>
Date:	Thu, 5 Jul 2007 16:44:54 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Yasunori Goto <y-goto@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: x86_64 memory hotplug simulation support?

Hi.

On Thursday 05 July 2007 16:20:18 Yasunori Goto wrote:
> Hello. Nigel-san.
> 
> > I'm wondering whether anyone has patches lying around that might be useful 
for 
> > simulating memory hotplug on x86_64. Goggling has revealed some old x86 
> > patches, but that's all.
> 
> I'm not sure what "simulation" means.
> Could you tell me how/what do you expect memory hotplug
> simulation exactly?
> 
> Memory hot-add code is included in kernel. And, remove(unplug) code
> has developed (and hopefully, it will be merged to -mm after
> some cleanups, I think.)
> 
> I would like to make sure what is necessary.

Thanks for your reply. Please, just call me Nigel :). I saw a patch that Dave 
Hansen had posted, back around the time of 2.6.11 iirc. It was for x86, and 
(so far as I understand) allowed a person who doesn't really have 
hotpluggable memory to make their computer pretend that it does.

Just in case I'm not being clear enough, let me get more concrete. I have had 
some code for a while that uses bitmaps to simulate page flags, without 
needing to take up those precious bits in page->flags. I've begun to add 
support for memory hotplugging, in the hope that I can make it general enough 
that it will be useful for more than just suspend2. To do that, I'd like to 
be able to test the memory hotplugging paths, without needing to actually 
have hotpluggable memory. I do have an x86 desktop I could work on, but would 
prefer to do it on my x86_64 laptop if I can.

Regards,

Nigel
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