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

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Message-ID: <alpine.DEB.2.00.1011181316290.26680@chino.kir.corp.google.com>
Date:	Thu, 18 Nov 2010 13:19:27 -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 Thu, 18 Nov 2010, Shaohui Zheng wrote:

> On Wed, Nov 17, 2010 at 01:10:50PM -0800, David Rientjes wrote:
> > I don't understand why that's a requirement, NUMA emulation is a seperate 
> > feature.  Although both are primarily used to test and instrument other VM 
> > and kernel code, NUMA emulation is restricted to only being used at boot 
> > to fake nodes on smaller machines and can be used to test things like the 
> > slab allocator.  The NUMA hotplug emulator that you're developing here is 
> > primarily used to test the hotplug callbacks; for that use-case, it seems 
> > particularly helpful if nodes can be hotplugged of various sizes and node 
> > ids rather than having static characteristics that cannot be changed with 
> > a reboot.
> > 
> I agree with you. the early emulator do the same thing as you said, but there 
> is already NUMA emulation to create fake node, our emulator also creates 
> fake nodes. We worried about that we will suffer the critiques from the community,
> so we drop the original degsin.
> 
> I did not know whether other engineers have the same attitude with you. I think 
> that I can publish both codes, and let the community to decide which one is prefered.
> 
> In my personal opinion, both methods are acceptable for me.
> 

The way that I've proposed it in my email to Dave was different: we use 
the memory hotplug interface to add and online the memory only after an 
interface has been added that will change the node mappings to 
first_unset_node(node_online_map).  The memory hotplug interface may 
create a new pgdat, so this is the node creation mechanism that should be 
used as opposed to those in NUMA emulation.
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