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

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Message-ID: <alpine.DEB.2.00.1011181321470.26680@chino.kir.corp.google.com>
Date:	Thu, 18 Nov 2010 13:24:52 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shaohui Zheng <shaohui.zheng@...el.com>
cc:	Paul Mundt <lethal@...ux-sh.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	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 Thu, 18 Nov 2010, Shaohui Zheng wrote:

> in our draft patch, we re-setup nr_node_ids when CONFIG_ARCH_MEMORY_PROBE enabled 
> and mem=XXX was specified in grub. we set nr_node_ids as MAX_NUMNODES + 1, because
>  we do not know how many nodes will be hot-added through memory/probe interface. 
>  it might be a little wasting of memory.
> 

nr_node_ids need not be set to anything different at boot, the 
MEM_GOING_ONLINE callback should be used for anything (like the slab 
allocators) where a new node is introduced and needs to be dealt with 
accordingly; this is how regular memory hotplug works, we need no 
additional code in this regard because it's emulated.  If a subsystem 
needs to change in response to a new node going online and doesn't as a 
result of using your emulator, that's a bug and either needs to be fixed 
or prohibited from use with CONFIG_MEMORY_HOTPLUG.

(See the MEM_GOING_ONLINE callback in mm/slub.c, for instance, which deals 
only with the case of node hotplug.)
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