Subject: Re: [PATCH] memory hotplug disable boot option
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Greg KH <gregkh@suse.de>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Nathan Fontenot <nfont@austin.ibm.com>,
       Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Thu, 01 Jul 2010 06:23:15 -0700
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On Thu, 2010-07-01 at 09:31 +0900, KAMEZAWA Hiroyuki wrote:
> 
> Considering briefly, how about this compact layout ?
> 
> /sys/devices/system/memory/:
>                             list, hide, show, memoryX...
> 
> list: // show available memory index list.
>   #cat list
>    0 1 2 ....10000...
> 
> show: //an interface to enable the interface.
>   #echo INDEX > memory_index
>   will create memoryINDEX diretory.
> 
> hide: //an interface to hide the interface.
>   #echo INDEX > memory_hide
>   will remove memoryINDEX sysfs directory.

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.

-- Dave

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