On 20/11/2020 01:20, Matthew Wilcox wrote: > 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. Ah, really, missed min() with PAGE_SIZE in bvec_iter_len(), then it's a stupid statement. Thanks! Are there many users of that? All these iterators are a huge burden, just to count one 4KB page in bvec it takes 2% of CPU time for me. -- Pavel Begunkov
