I really don't think that these comments are all that useful. A big comment near the bi_io_vec field defintion explaining the rules for access would be a lot better.
- [PATCH v3 00/49] block: support multipage bvec Ming Lei
- [PATCH v3 01/49] block: drbd: comment on direct acc... Ming Lei
- Re: [PATCH v3 01/49] block: drbd: comment on di... Christoph Hellwig
- [PATCH v3 15/49] bvec_iter: introduce BVEC_ITER_ALL... Ming Lei
- [PATCH v3 13/49] btrfs: comment on direct access bv... Ming Lei
- [PATCH v3 14/49] block: bounce: avoid direct access... Ming Lei
- [PATCH v3 20/49] block: introduce bio_for_each_segm... Ming Lei
- Re: [PATCH v3 20/49] block: introduce bio_for_e... Christoph Hellwig
- [PATCH v3 24/49] block: use bio_for_each_segment_mp... Ming Lei
- [PATCH v3 27/49] block: bio: introduce single/multi... Ming Lei
- [PATCH v3 34/49] md: raid1: convert to bio_for_each... Ming Lei
- [PATCH v3 40/49] ext4: convert to bio_for_each_segm... Ming Lei
- [PATCH v3 45/49] fs: crypto: convert to bio_for_eac... Ming Lei