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

On 11/23/21 9:39 AM, Christoph Hellwig wrote:

quoted

+	/* 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.

quoted

+
+	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