On Wed, Aug 07, 2013 at 02:54:09PM -0700, Kent Overstreet wrote:

_However_, I have more patches (that depend on this patch series) to get
that back - segment merging improvements that get rid of
bi_seg_front_size, bi_seg_back_size, and bi_phys_segments. Once all that
is in it should be a net reduction to the size of struct bio.

What is preventing you from sending those out as well?  While it's not
absolutely nessecary it would certainly be good if we'd avoid a struct
bio size regression.