Re: [PATCHv2 1/1] block: introduce content activity based ioprio

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jan 24, 2024 at 04:53:34PM +0800, zhaoyang.huang wrote:
>  void __bio_add_page(struct bio *bio, struct page *page,
>  		unsigned int len, unsigned int off)
>  {
> +	int class, level, hint, activity;
> +
> +	class = IOPRIO_PRIO_CLASS(bio->bi_ioprio);
> +	level = IOPRIO_PRIO_LEVEL(bio->bi_ioprio);
> +	hint = IOPRIO_PRIO_HINT(bio->bi_ioprio);
> +	activity = IOPRIO_PRIO_ACTIVITY(bio->bi_ioprio);
> +
>  	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
>  	WARN_ON_ONCE(bio_full(bio, len));
>  
>  	bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, off);
>  	bio->bi_iter.bi_size += len;
>  	bio->bi_vcnt++;
> +	activity += bio_page_if_active(bio, page, IOPRIO_NR_ACTIVITY);
> +	bio->bi_ioprio = IOPRIO_PRIO_VALUE_ACTIVITY(class, level, hint, activity);

If you need to touch anything in the block layer I/O path
you're doign this wrong.  The file system that is submitting the
I/O needs to be in control of the priorities.
must not hack the assignment behind the