On 2/27/19 8:24 PM, Ming Lei wrote:

bio_for_each_bvec is used in fast path of bio splitting and sg mapping,
and what we want to do is to iterate over multi-page bvecs, instead of pages.
However, bvec_iter_advance() is invisble for this requirement, and
always advance by page size.

This way isn't efficient for multipage bvec iterator, also bvec_iter_len()
isn't as fast as mp_bvec_iter_len().

So advance by multi-page bvec's length instead of page size for bio_for_each_bvec().

More than 1% IOPS improvement can be observed in io_uring test on null_blk.

Thanks Ming, I tested this last night with good results.

-- 
Jens Axboe