Re: [PATCH V10 08/19] btrfs: move bio_pages_all() to btrfs

[Christoph Hellwig]

On Thu, Nov 15, 2018 at 04:52:55PM +0800, Ming Lei wrote:
> BTRFS is the only user of this helper, so move this helper into
> BTRFS, and implement it via bio_for_each_segment_all(), since
> bio->bi_vcnt may not equal to number of pages after multipage bvec
> is enabled.

btrfs only uses the value to check if it is larger than 1.  No amount
of multipage bio merging should ever make bi_vcnt go from 0 to 1 or
vice versa.