linux-kernel - Re: [2/8,v3] NUMA Hotplug Emulator: infrastructure of NUMA hotplug emulation

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Message-ID: <alpine.DEB.2.00.1011162359160.17408@chino.kir.corp.google.com>
Date:	Wed, 17 Nov 2010 00:16:47 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shaohui Zheng <shaohui.zheng@...el.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...ux.intel.com,
	shaohui.zheng@...ux.intel.com, Yinghai Lu <yinghai@...nel.org>,
	Haicheng Li <haicheng.li@...el.com>
Subject: Re: [2/8,v3] NUMA Hotplug Emulator: infrastructure of NUMA hotplug
 emulation

On Wed, 17 Nov 2010, shaohui.zheng@...el.com wrote:

> From: Haicheng Li <haicheng.li@...el.com>
> 
> NUMA hotplug emulator introduces a new node state N_HIDDEN to
> identify the fake offlined node. It firstly hides RAM via E820
> table and then emulates fake offlined nodes with the hidden RAM.
> 

Hmm, why can't you use numa=hide to hide a specified quantity of memory 
from the kernel and then use the add_memory() interface to hot-add the 
offlined memory in the desired quantity?  In other words, why do you need 
to track the offlined nodes with a state?

The userspace interface would take a desired size of hidden memory to 
hot-add and the node id would be the first_unset_node(node_online_map).

> After system bootup, user is able to hotplug-add these offlined
> nodes, which is just similar to a real hardware hotplug behavior.
> 
> Using boot option "numa=hide=N*size" to fake offlined nodes:
> 	- N is the number of hidden nodes
> 	- size is the memory size (in MB) per hidden node.
> 

size should be parsed with memparse() so users can specify 'M' or 'G', it 
would even make your parsing code simpler.
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