If it is measurable I'll take another stab at using memory from
__get_free_pages() for the ringbuffer. That really would be the ideal
solution.

No, then you'll run into high order allocation failures with rings that
don't fit in a single page.

The other reason I wanted to do this was for the aio attributes stuff -
for return values, I think the only sane way is for the return values to
go in the ringbuffer, which means records are no longer fixed size so
dealing with pages is even more of a pain.

Then let's see that, please.

And can we please stop calling them attributes?  They're inputs and
outputs that change behaviour -- they're interfaces.

And no, just for the record, I don't think generic packed variable size
structs are worth the trouble.

If we're going to do a generic interface extension mechanism then we
should put it in its own well thought out system calls, not staple it on
to the side of aio because it's there.  It's a really crummy base to
work from.

- z