Re: [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec

[Matthew Wilcox]

On Fri, Nov 20, 2020 at 02:25:08AM +0000, Pavel Begunkov wrote:
> On 20/11/2020 02:22, Ming Lei wrote:
> > iov_iter_npages(bvec) still can be improved a bit by the following way:
> 
> Yep, was doing exactly that, +a couple of other places that are in my way.

Are you optimising the right thing here?  Assuming you're looking at
the one in do_blockdev_direct_IO(), wouldn't we be better off figuring
out how to copy the bvecs directly from the iov_iter into the bio
rather than calling dio_bio_add_page() for each page?