block_size_bytes:  The size of each memory section (in hex)

memoryXXXX: Each directory contains individual information about
	that memory section.  The number associated with the
	memory section is arbitrary, and should not be
	used for any calculations, it is a useless tag.

memoryXXXX/phys_index: multiply this by block_size_bytes and you
	can calculate the starting physical address of this
	memory section.  This is so that you can directly 
	correlate the memoryXXXX directory with any probe that
	you've issued.

probe: The user may write a physical address into this file to
	initate a hot-addition of a new memory section.  

echo 0x00000000 > /sys/devices/system/memory/probe
memory_probe_store()
  add_memory()
	  __add_pages()
	  __add_section()
		allocate section memmap
		lock zone
		register_new_memory()
			add_memory_block()
			register_memory()
				create kobject -> generates hotplug event
			sysfs create files()
		unlock zone

/sbin/hotplug sees "ADD" event, calls:

#!/bin/sh
# goes in /etc/hotplug.d/memory/onlinenow.hotplug
if [ "$ACTION" != "add" ]; then
	exit 0;
fi
while ! [ -f $SYSFS/$DEVPATH/state ]; do
	sleep 0.1;
done
echo online > "$SYSFS/$DEVPATH/state"

store_mem_state()
	memory_block_change_state()
		memory_block_action()
		|------>online_pages()
		|		online_page()
		|			__free_page()
		\------>remove_memory()
				__remove_pages()
					capture_page_range()
					unregister_memory_section()
						-> generates unplug event