nvme: Allow larger user request sizes

[imp]

Summary

We have a small buffer for pages on the stack, but if the user wants to
do an I/O larger than this we currently fail w/o a way for the user to
know the max size. It's not hard to allocate an array for the uncommon
case of very large I/Os, and the performance advantage of the array is
small in that case anyway.

Sponsored by: Netflix

[jhb]

sys/dev/nvme/nvme_ctrlr.c

1367

Having the constant checked here separately from the declaration of the array seems a bit fragile. It might be nicer if this function took an extra parameter holding the count of pages instead (using nitems() in the caller) so that if you change the size of the array in the caller for some reason, this function wouldn't be out of sync.

Actually, you have that if you just check maxpages here instead of the hard-coded constant? Right now max_pages isn't used.

1521

This one needs to pass nitems(upages_small). You fixed this above, but not in this function.

[imp]

sys/dev/nvme/nvme_ctrlr.c

1367

Yes. This is why the goofs elsewhere aren't as fatal as they should be.
It should be max_pages.

1521

this was fixed in a followup.