Re: [PATCH 1/2] block: Make __submit_bio_noacct() preserve the bio submission order

[Keith Busch <kbusch@kernel.org>]

On Wed, Jun 11, 2025 at 09:46:31AM +0900, Damien Le Moal wrote:
> On 6/11/25 8:18 AM, Keith Busch wrote:
> > 
> > I think you could just prep the encryption at the point the bio is split
> > to its queue's limits, and then all you need to do after that is ensure
> > the limits don't exceed what the fallback requires (which appears to
> > just be a simple segment limitation). It looks like most of the bio
> > based drivers split to limits already.
> 
> Nope, at least not DM, and by that, I mean not in the sense of splitting BIOs
> using bio_split_to_limits(). The only BIOs being split are "abnormal" ones,
> such as discard.
> 
> That said, DM does split the BIOs through cloning and also has the "accept
> partial" thing, which is used in many places and allows DM target drivers to
> split BIOs as they are received, but not necessarilly based on the device queue
> limits (e.g. dm-crypt splits reads and writes using an internal
> max_read|write_size limit).
> 
> So inline crypto on top of a DM/bio-based device may need some explicit
> splitting added in dm.c (__max_io_len() maybe ?).

Ah, thanks for pointing that out! In that case, could we have dm
consider the bio "abnormal" when bio_has_crypt_ctx(bio) is true? That
way it does the split-to-limits for these, and dm appears to do that
action very early before its own split/clone actions on the resulting
bio.