Is this guaranteed to improve performance for everyone?
If there are realistic configurations where it would make performance
worse, it needs to be configurable.
Hooking into extended versions of the multipath load balancing
modules (and adding a new proximity one) might indeed be another approach.
For upstream the PRINTKs would need to come out of course.
(We do have DMDEBUG though.)
If there are any necessary statistics that can't be gleaned with
'iostat' they could be published via blktrace or 'dmsetup status'.
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