Re: [PATCH 1/3] block: move io_context creation into where it's needed

[Jens Axboe <axboe@kernel.dk>]

On 11/23/21 9:39 AM, Christoph Hellwig wrote:
>> +	/* create task io_context, if we don't have one already */
>> +	if (unlikely(!current->io_context))
>> +		create_task_io_context(current, GFP_ATOMIC, rq->q->node);
> 
> Wouldn't it be nicer to have an interface that hides the check
> and the somewhat pointless current argument?  And name that with a
> blk_ prefix?

Yeah, we can do that.

>> +
>> +	blk_mq_sched_assign_ioc(rq);
> 
> But thinking about this a little more:
> 
> struct io_context has two uses, one is the unsigned short ioprio,
> and the other is the whole bfq mess.
> 
> Can't we just split the ioprio out (we'll find a hole somewhere
> in task_struct) and then just allocate the io_context in
> blk_mq_sched_assign_ioc, which would also avoid the pointless
> ioc_lookup_icq on a newly allocated io_context.  I'd also really
> expect blk_mq_sched_assign_ioc to be implemented in blk-ioc.c.

It would be nice to decouple ioprio from the io_context, and just
leave the io_context for BFQ essentially.

I'll give it a shot.

> While we're at it: bfq_bic_lookup is a really weird helper which
> gets passed an unused bfqd argument.

Unsurprising.

-- 
Jens Axboe