Re: [PATCH v2 4/4] block/mq-deadline: Prevent zoned write reordering due to I/O prioritization

Christoph Hellwig
2023-12-20T03:53:51Z

On Wed, Dec 20, 2023 at 10:28:37AM +0900, Damien Le Moal wrote:
> zone, and as I said before, since doing that is nonsensical, getting the IOs to
> fail is fine by me. The user will then be aware that this should not be done.
>
> f2fs has a problem with that though as that leads to write errors and FS going
> read-only (I guess). btrfs will not have this issue because it uses zone append.
> Need to check dm-zoned as their may be an issue there.
>
> So what about what I proposed in an earlier email: introduce a bio flag "ignore
> ioprio" that causes bio_set_ioprio() to not set any IO priority and have f2fs
> set that flag for any zone write BIO it issues ? That will solve your f2fs issue
> without messing up good use cases.

How can this even be a problem for f2f2 upsteam where f2fs must only
have a single write per zone outstanding? I really don't want crap
in the block layer to work around a known broken model (multiple
outstanding WRITE commands per zone) that because it's so known broken
isn't even merged upstream.