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

On Thu, 2 Dec 2010, Shaohui Zheng wrote:

quoted

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From: Shaohui Zheng <redacted>

Implement a debugfs inteface /sys/kernel/debug/mem_hotplug/probe for meomory hotplug
emulation.  it accepts the same parameters like
/sys/devices/system/memory/probe.

NACK, we don't need two interfaces to do the same thing.  

You may not know the background, the sysfs memory/probe interface is a general
interface.  Even through we have a debugfs interface, we should still keep it.

For test purpose, the sysfs is enough, according to the comments from Greg & Dave,
we create the debugfs interface.

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.