On Wed, Nov 21, 2018 at 11:31:36PM +0800, Ming Lei wrote: > > But while looking over this I wonder why we even need the max_seg_len > > here. The only thing __bvec_iter_advance does it to move bi_bvec_done > > and bi_idx forward, with corresponding decrements of bi_size. As far > > as I can tell the only thing that max_seg_len does is that we need > > to more iterations of the while loop to archive the same thing. > > > > And actual bvec used by the caller will be obtained using > > bvec_iter_bvec or segment_iter_bvec depending on if they want multi-page > > or single-page variants. > > Right, we let __bvec_iter_advance() serve for both multi-page and single-page > case, then we have to tell it via one way or another, now we use the constant > of 'max_seg_len'. > > Or you suggest to implement two versions of __bvec_iter_advance()? No - I think we can always use the code without any segment in bvec_iter_advance. Because bvec_iter_advance only operates on the iteractor, the generation of an actual single-page or multi-page bvec is left to the caller using the bvec_iter_bvec or segment_iter_bvec helpers. The only difference is how many bytes you can move the iterator forward in a single loop iteration - so if you pass in PAGE_SIZE as the max_seg_len you just will have to loop more often for a large enough bytes, but not actually do anything different.
