Re: [PATCH 1/3] block: Add iocontext priority to request

[Tejun Heo <tj@kernel.org>]

Hello, Adam.

On Tue, Oct 04, 2016 at 08:49:18AM -0700, Adam Manzanares wrote:
> > I wonder whether the right thing to do is adding bio->bi_ioprio which
> > is initialized on bio submission and carried through req->ioprio.
> 
> I looked around and thought about this and I'm not sure if this will help. 
> I dug into the bio submission code and I thought generic_make_request was 
> the best place to save the ioprio information. This is quite close in 
> the call stack to init_request_from bio. Bcache sets the bio priority before 
> the submission, so we would have to check to see if the bio priority was 
> valid on bio submission leaving us with the same problem. Leaving the 
> priority in the upper bits of bio->bi_rw is fine with me. It may help to 
> have the bio->bi_ioprio for clarity, but I think we will still face the 
> issue of having to check if this value is set when we submit the bio or 
> init the request so I'm leaning towards leaving it as is.

I see.  Thanks for looking into it.  It's icky that we don't have a
clear path of propagating ioprio but let's save that for another day.

-- 
tejun