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

[Matthew Wilcox]

On Thu, Nov 19, 2020 at 11:24:38PM +0000, Pavel Begunkov wrote:
> The block layer spends quite a while in iov_iter_npages(), but for the
> bvec case the number of pages is already known and stored in
> iter->nr_segs, so it can be returned immediately as an optimisation

Er ... no, it doesn't.  nr_segs is the number of bvecs.  Each bvec can
store up to 4GB of contiguous physical memory.