Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:49008 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390653AbeKVUys (ORCPT ); Thu, 22 Nov 2018 15:54:48 -0500 Date: Thu, 22 Nov 2018 18:15:28 +0800 From: Ming Lei To: Christoph Hellwig Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Theodore Ts'o , Omar Sandoval , Sagi Grimberg , Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com Subject: Re: [PATCH V11 03/19] block: introduce bio_for_each_bvec() Message-ID: <20181122101527.GB27273@ming.t460p> References: <20181121032327.8434-1-ming.lei@redhat.com> <20181121032327.8434-4-ming.lei@redhat.com> <20181121133244.GB1640@lst.de> <20181121153135.GB19111@ming.t460p> <20181121161025.GB4977@lst.de> <20181121171217.GA6259@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181121171217.GA6259@lst.de> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, Nov 21, 2018 at 06:12:17PM +0100, Christoph Hellwig wrote: > On Wed, Nov 21, 2018 at 05:10:25PM +0100, Christoph Hellwig wrote: > > 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. > > FYI, this patch reverts the max_seg_len related changes back to where > we are in mainline, and as expected everything works fine for me: > > diff --git a/include/linux/bio.h b/include/linux/bio.h > index e5b975fa0558..926550ce2d21 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -137,24 +137,18 @@ static inline bool bio_full(struct bio *bio) > for (i = 0, iter_all.idx = 0; iter_all.idx < (bio)->bi_vcnt; iter_all.idx++) \ > bvec_for_each_segment(bvl, &((bio)->bi_io_vec[iter_all.idx]), i, iter_all) > > -static inline void __bio_advance_iter(struct bio *bio, struct bvec_iter *iter, > - unsigned bytes, unsigned max_seg_len) > +static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter, > + unsigned bytes) > { > iter->bi_sector += bytes >> 9; > > if (bio_no_advance_iter(bio)) > iter->bi_size -= bytes; > else > - __bvec_iter_advance(bio->bi_io_vec, iter, bytes, max_seg_len); > + bvec_iter_advance(bio->bi_io_vec, iter, bytes); > /* TODO: It is reasonable to complete bio with error here. */ > } > > -static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter, > - unsigned bytes) > -{ > - __bio_advance_iter(bio, iter, bytes, PAGE_SIZE); > -} > - > #define __bio_for_each_segment(bvl, bio, iter, start) \ > for (iter = (start); \ > (iter).bi_size && \ > @@ -168,7 +162,7 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter, > for (iter = (start); \ > (iter).bi_size && \ > ((bvl = bio_iter_mp_iovec((bio), (iter))), 1); \ > - __bio_advance_iter((bio), &(iter), (bvl).bv_len, BVEC_MAX_LEN)) > + bio_advance_iter((bio), &(iter), (bvl).bv_len)) > > /* returns one real segment(multi-page bvec) each time */ > #define bio_for_each_bvec(bvl, bio, iter) \ > diff --git a/include/linux/bvec.h b/include/linux/bvec.h > index cab36d838ed0..138b4007b8f2 100644 > --- a/include/linux/bvec.h > +++ b/include/linux/bvec.h > @@ -25,8 +25,6 @@ > #include > #include > > -#define BVEC_MAX_LEN ((unsigned int)-1) > - > /* > * was unsigned short, but we might as well be ready for > 64kB I/O pages > */ > @@ -102,8 +100,8 @@ struct bvec_iter_all { > .bv_offset = segment_iter_offset((bvec), (iter)), \ > }) > > -static inline bool __bvec_iter_advance(const struct bio_vec *bv, > - struct bvec_iter *iter, unsigned bytes, unsigned max_seg_len) > +static inline bool bvec_iter_advance(const struct bio_vec *bv, > + struct bvec_iter *iter, unsigned bytes) > { > if (WARN_ONCE(bytes > iter->bi_size, > "Attempted to advance past end of bvec iter\n")) { > @@ -112,18 +110,12 @@ static inline bool __bvec_iter_advance(const struct bio_vec *bv, > } > > while (bytes) { > - unsigned segment_len = segment_iter_len(bv, *iter); > - > - if (max_seg_len < BVEC_MAX_LEN) > - segment_len = min_t(unsigned, segment_len, > - max_seg_len - > - bvec_iter_offset(bv, *iter)); > + unsigned iter_len = bvec_iter_len(bv, *iter); > + unsigned len = min(bytes, iter_len); It may not work to always use bvec_iter_len() here, and 'segment_len' should be max length of the passed 'bv', however we don't know if it is single-page or mutli-page bvec if no one tells us. Thanks, Ming