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

[Zhaoyang Huang]

On Wed, Jan 24, 2024 at 5:20 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> 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
Please correct me if I am wrong. According to my understanding,
bio(request)'s ioprio is set via either task's scheduler priority or
blkcg's priority during submit_bio, that is, there is no explicit
operation over ioprio from the file system so far. Furthermore, this
commit is actually an add-on feature which is not against the current
way of setting ioprio.