[RFC 1/3] nvme: skip block cgroups for passthrough commands

[Keith Busch]

On Wed, May 03, 2023 at 09:25:21AM -0600, Keith Busch wrote:
> On Wed, May 03, 2023 at 07:04:14AM +0200, Christoph Hellwig wrote:
> > On Mon, May 01, 2023 at 08:33:04AM -0700, Keith Busch wrote:
> > > From: Keith Busch <kbusch at kernel.org>
> > > 
> > > Passthrough requests don't go through the submit_bio() path, so all the
> > > overhead of setting up the bio's cgroup is wasted cycles. Provide a path
> > > to skip this setup.
> > 
> > These days we should not need to set bi_bdev at all for passthrough,
> > so I think we can just drop the assingment.
> 
> We can't really skip it for polling since that needs a bio with a
> bdev. I'll take another shot at detandling that requirement.

I've got a new version ready to go that removes the bio and bi_dev
requirement for polling uring commands, but passthrough still needs to
set bi_bdev for metadata since it's used in bio_integrity_add_page(). I
suppose we could have that just take the queue limits directly instead
of extracting them from an assumed bi_dev.