Re: [PATCH] ublk: remove io_cmds list in ublk_queue

[Jens Axboe <axboe@kernel.dk>]

On 3/18/25 12:43 PM, Uday Shankar wrote:
> On Tue, Mar 18, 2025 at 12:22:57PM -0600, Jens Axboe wrote:
>>>  struct ublk_rq_data {
>>> -	struct llist_node node;
>>> -
>>>  	struct kref ref;
>>>  };
>>
>> Can we get rid of ublk_rq_data then? If it's just a ref thing, I'm sure
>> we can find an atomic_t of space in struct request and avoid it. Not a
>> pressing thing, just tossing it out there...
> 
> Yeah probably - we do need a ref since one could complete a request
> concurrently with another code path which references it (user copy and
> zero copy). I see that struct request has a refcount in it already,

Right, at least with the current usage, we still do need that kref, or
something similar. I would've probably made it just use refcount_t
though, rather than rely on the indirect calls. kref doesn't really
bring us anything here in terms of API.

> though I don't see any examples of drivers using it. Would it be a bad
> idea to try and reuse that?

We can't reuse that one, and it's not for driver use - purely internal.
But I _think_ you could easily grab space in the union that has the hash
and ipi_list for it. And then you could dump needing this extra data per
request.

-- 
Jens Axboe