[dm-devel] [PATCH V5 05/12] block: add new field into 'struct bvec_iter'

[Christoph Hellwig]

I don't like where this is going.

I think the model of storing the polling cookie in the bio is useful,
but:

 (1) I think having this in the iter is a mess.  Can you measure if
     just marking bvec_iter __packed will generate much worse code
     at all anymore?  If not we can just move this into the bio
     If it really generates much worse code I think you need to pick
     a different name as  as that i really confusing vs the bio field
     of the same name that is used entirely differenly.  Similarly
     the bio_get_private_data and bio_set_private_data helpers are
     entirely misnamed, as the names suggest they deal with the
     bi_private field in struct bio.  I actually suspect not having
     these helpers would be much preferable
 (2) once we do have the cookie in the bio we need to take advantage
     of that properly.  That is stop returning the cookie up the stack
     as we do right now but just rely on the bio, which will clean up
     tons of crap.