Re: Read-only Mapping of Program Text using Large THP Pages

[Keith Busch <keith.busch@intel.com>]

On Wed, Feb 20, 2019 at 06:43:46AM -0800, Matthew Wilcox wrote:
> What NVMe doesn't have is a way for the host to tell the controller
> "Here's a 2MB sized I/O; bytes 40960 to 45056 are most important to
> me; please give me a completion event once those bytes are valid and
> then another completion event once the entire I/O is finished".
> 
> I have no idea if hardware designers would be interested in adding that
> kind of complexity, but this is why we also have I/O people at the same
> meeting, so we can get these kinds of whole-stack discussions going.

We have two unused PRP bits, so I guess there's room to define something
like a "me first" flag. I am skeptical we'd get committee approval for
that or partial completion events, though.

I think the host should just split the more important part of the transfer
into a separate command. The only hardware support we have to prioritize
that command ahead of others is with weighted priority queues, but we're
missing driver support for that at the moment.