Re: [RFC PATCH 1/1] block: introduce activity based ioprio

[Bart Van Assche]

On 1/17/24 01:23, zhaoyang.huang wrote:
> +static enum dd_prio dd_req_ioprio(struct request *rq)
> +{
> +	enum dd_prio prio;
> +	const u8 ioprio_class = dd_rq_ioclass(rq);
> +#ifdef CONFIG_ACTIVITY_BASED_IOPRIO
> +	struct bio *bio;
> +	struct bio_vec bv;
> +	struct bvec_iter iter;
> +	struct page *page;
> +	int gen = 0;
> +	int cnt = 0;
> +
> +	if (req_op(rq) == REQ_OP_READ) {
> +		__rq_for_each_bio(bio, rq) {
> +			bio_for_each_bvec(bv, bio, iter) {
> +				page = bv.bv_page;
> +				gen += PageWorkingset(page) ? 1 : 0;
> +				cnt++;
> +			}
> +		}
> +		prio = (gen >= cnt / 2) ? ioprio_class_to_prio[IOPRIO_CLASS_RT] :
> +			ioprio_class_to_prio[ioprio_class];
> +	} else
> +		prio = ioprio_class_to_prio[ioprio_class];
> +#else
> +	prio = ioprio_class_to_prio[ioprio_class];
> +#endif
> +	return prio;
> +}

I don't like it that code is introduced in the mq-deadline scheduler
that accesses page cache information. Isn't that a layering violation?
Additionally, this approach only works for buffered I/O and not for
direct I/O. Shouldn't the I/O submitter set the I/O priority instead of
deciding the I/O priority in the mq-deadline scheduler?

Bart.