As written, blk_recount_segments() requires the size of physically contiguous bio_vecs to not exceed the maximum virtually contiguous region. This seems to be done in order to optimize the calculation of the hw_seg_size variable in the algorithm. The code in blk_phys_contig_segment() does not force this requirement for physically contiguous regions? Why the inconsistency? Also, why do the initial back and front merges in __make_request() done by ll_back_merge_fn() and ll_front_merge_fn() respectively only consider virtually contiguous bio_vecs while the secondary merging done in __make_request() by ll_merge_reqeusts_fn() considers both physical and virtual bio_vec contiguity? Off topic only a bit, but also important to bio_vec merging -- should not an indication of the high physical page frame number, above which all bio pages are bounced, be included in the device-mapper io_restrictions structure used by blk_recount_segments() for all I/O to a device-mapper mapped device? Otherwise, isn't it possible for blk_recount_segments() to include bio_vec pages in a physical segment even if they may end up getting bounced if the bio is sent, by say the multipath target driver, to a different target device whose queue has a bounce_pfn value less than the one used by blk_recount_segments() with the mapped device?
