linux-kernel - Re: [PATCH] memory hotplug disable boot option

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Date:	Tue, 06 Jul 2010 08:33:05 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Nathan Fontenot <nfont@...tin.ibm.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Greg KH <gregkh@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] memory hotplug disable boot option

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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