linux-kernel - Re: [8/8, v6] NUMA Hotplug Emulator: implement debugfs interface for memory probe

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Date:	Thu, 2 Dec 2010 08:27:16 +0800
From:	Shaohui Zheng <shaohui.zheng@...el.com>
To:	"shaohui.zheng@...ux.intel.com" <shaohui.zheng@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>
Cc:	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, dave@...ux.vnet.ibm.com,
	gregkh@...e.de, Haicheng Li <haicheng.li@...el.com>
Subject: Re: [8/8, v6] NUMA Hotplug Emulator: implement debugfs interface
 for memory probe

> 
> I doubt either Greg or Dave suggested adding duplicate interfaces for the 
> same functionality.
> 
> The difference is that we needed to add the add_node interface in a new 
> mem_hotplug debugfs directory because it's only useful for debugging 
> kernel code and, thus, doesn't really have an appropriate place in sysfs.  
> Nobody is going to use add_node unless they lack hotpluggable memory 
> sections in their SRAT and want to debug the memory hotplug callers.  For 
> example, I already wrote all of this node hotplug emulation stuff when I 
> wrote the node hotplug support for SLAB.
> 
> Memory hotplug, however, does serve a non-debugging function and is 
> appropriate in sysfs since this is how people hotplug memory.  It's an ABI 
> that we can't simply remove without deprecation over a substantial period 
> of time and in this case it doesn't seem to have a clear advantage.  We 
> need not add special emulation support for something that is already 
> possible for real systems, so adding a duplicate interface in debugfs is 
> inappropriate.

so we should still keep the sysfs memory/probe interface without any modifications,
but for the debugfs mem_hotplug/probe interface, we can add the memory region 
to a desired node. It is an extention for the sysfs memory/probe interface, it can 
be used for memory hotplug emulation. Do I understand it correctly?

-- 
Thanks & Regards,
Shaohui

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