Re: [PATCH V11 03/19] block: introduce bio_for_each_bvec()

Ming Lei
2018-11-22T14:58:20Z

On Thu, Nov 22, 2018 at 11:30:33AM +0100, Christoph Hellwig wrote:
> Btw, this patch instead of the plain rever might make it a little
> more clear what is going on by skipping the confusing helper altogher
> and operating on the raw bvec array:
>
>
> 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..7d0f9bdb6f05 100644
> --- a/include/linux/bvec.h
> +++ b/include/linux/bvec.h
> @@ -25,8 +25,6 @@
> #include <linux/errno.h>
> #include <linux/mm.h>
>
> -#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")) {
> @@ -112,20 +110,15 @@ 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));
> + const struct bio_vec *cur = bv + iter->bi_idx;
> + unsigned len = min3(bytes, iter->bi_size,
> + cur->bv_len - iter->bi_bvec_done);
>
> - segment_len = min(bytes, segment_len);
> -
> - bytes -= segment_len;
> - iter->bi_size -= segment_len;
> - iter->bi_bvec_done += segment_len;
> + bytes -= len;
> + iter->bi_size -= len;
> + iter->bi_bvec_done += len;
>
> - if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
> + if (iter->bi_bvec_done == cur->bv_len) {
> iter->bi_bvec_done = 0;
> iter->bi_idx++;
> }

I'd rather not do the optimization part in this patchset, given it doesn't
belong to this patchset, and it may decrease readability. So I plan to revert
the delta part in V12 first.

Thanks,
Ming