Subject: Re: [PATCH] memory hotplug disable boot option
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Nathan Fontenot <nfont@austin.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Greg KH <gregkh@suse.de>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       "Eric W. Biederman" <ebiederm@xmission.com>
In-Reply-To: <4C3349BF.7030104@austin.ibm.com>
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	 <1277827384.8354.3413.camel@nimitz>	<20100629180415.GB1240@suse.de>
	 <20100630093251.a30ed1e0.kamezawa.hiroyu@jp.fujitsu.com>
	 <20100630154755.GB12158@suse.de>
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Date: Tue, 06 Jul 2010 08:33:05 -0700
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On Tue, 2010-07-06 at 10:20 -0500, Nathan Fontenot wrote:
> On 07/01/2010 08:23 AM, Dave Hansen wrote:
> > 
> > I was thinking more along the lines of just taking adjacent sections and
> > merging them.  We'll need a new "end address" or size file.  Maybe
> > "end_phys_index" or something similar.
> > 
> > Such a beast would not fix all of the pathological cases, like where
> > only every other 16MB section is populated with RAM, but I don't think
> > those are very common at all, especially in cases where there's a lot of
> > RAM.  But, it also has a chance of being relatively backward-compatible.
> > In most cases, we may even be able to calculate a new phys_block_size
> > where everything fits evenly and be fully backward-compatible with the
> > old ABI.
> 
> Under this scenario were you thinking that all of the memory sections that
> reside under this memory block would then be acted upon as a whole.  For
> example would we allow users to hotplug individual memory sections included
> in th block, or would the memory block be acted upon as a whole?

I think we would need a mechanism that allowed the sysfs directories to
be broken down somehow.  If the merging is very successful, it could
lead to a case where no existing sysfs dir is a reasonable size to
remove.  That's what we'd have to avoid, so I think we'd _need_
splitting of some kind.


-- Dave

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