I have the reason to have to fill the node struct with 0 by memset.
The node is a part of node struct array (node_devices[]).
If we add empty release function for suppressing warning,
some data remains in the node struct after hot removing memory.
So if we re-hot adds the memory, the node struct is reused by
register_onde_node(). But the node struct has some data, because
it was not initialized with 0. As a result, more waning is shown
by the remained data at hot addinig memory as follows:

Even though you call memset(0) at offline. It doesn't guarantee the memory
keep 0 until online. E.g. physical memory exchange during offline, bit
corruption
by cosmic ray, etc. So, you should fill zero at online phase explicitly if need.

The basic hotplug design is: you should forget everything at offline
and you shouldn't
assume any initialized data at online.

Thanks.

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