On Wed, Dec 20, 2023 at 10:12 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Wed, Dec 20, 2023 at 05:27:14PM -0800, Song Liu wrote:
> > Upper layer (fs, etc.) may issue flush with something like:
> >
> > bio_reset(bio, bdev, REQ_OP_FLUSH);
> > bio->bi_end_io = xxx;
> > submit_bio(bio);
>
> No, they can't. REQ_OP_FLUSH is currently only used by request
> based drivers and only generated by the flush state machine.
Hmm... Then this call trace from bcachefs is the exception here:
bch2_journal_write=>
submit_bio=>
...
md_handle_request =>
raid5_make_request =>
chunk_aligned_read =>
raid5_read_one_chunk =>
> (Not that I particularly like this wart, I'd much prefer file systems
> to submit a REQ_OP_FLUSH than an empty write with a preflush flag,
> but that's not a trivial change).
Kent, I think we need to update how bcachefs issue flushes.
Thanks,
Song
