Given that pmem simply loops over an arbitrarily large bio I think we also need a threshold for which to allow nowait I/O. While it won't block for giant I/Os, doing all of them in the submitter context isn't exactly the idea behind the nowait I/O.
I'm not really sure what a good theshold would be, though. Btw, please also always add linux-block to the Cc list for block driver patches that are even the slightest bit about the block layer interface.
