Re: [PATCH V10 02/19] block: introduce bio_for_each_bvec()
From: Ming Lei <hidden>
Date: 2018-11-19 03:31:11
Also in:
dm-devel, linux-bcache, linux-block, linux-btrfs, linux-ext4, linux-fsdevel, linux-mm, linux-xfs, lkml
On Fri, Nov 16, 2018 at 02:30:28PM +0100, Christoph Hellwig wrote:
quoted
+static inline void __bio_advance_iter(struct bio *bio, struct bvec_iter *iter, + unsigned bytes, bool mp)I think these magic 'bool np' arguments and wrappers over wrapper don't help anyone to actually understand the code. I'd vote for removing as many wrappers as we really don't need, and passing the actual segment limit instead of the magic bool flag. Something like this untested patch:
I think this way is fine, just a little comment.
quoted hunk ↗ jump to hunk
diff --git a/include/linux/bio.h b/include/linux/bio.h index 277921ad42e7..dcad0b69f57a 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h@@ -138,30 +138,21 @@ static inline bool bio_full(struct bio *bio) 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, bool mp) + unsigned bytes, unsigned max_segment)
The new parameter should have been named as 'max_segment_len' or 'max_seg_len'.
quoted hunk ↗ jump to hunk
{ iter->bi_sector += bytes >> 9; if (bio_no_advance_iter(bio)) iter->bi_size -= bytes; else - if (!mp) - bvec_iter_advance(bio->bi_io_vec, iter, bytes); - else - mp_bvec_iter_advance(bio->bi_io_vec, iter, bytes); + __bvec_iter_advance(bio->bi_io_vec, iter, bytes, max_segment); /* 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, false); -} - -static inline void bio_advance_mp_iter(struct bio *bio, struct bvec_iter *iter, - unsigned bytes) -{ - __bio_advance_iter(bio, iter, bytes, true); + __bio_advance_iter(bio, iter, bytes, PAGE_SIZE); } #define __bio_for_each_segment(bvl, bio, iter, start) \@@ -177,7 +168,7 @@ static inline void bio_advance_mp_iter(struct bio *bio, struct bvec_iter *iter, for (iter = (start); \ (iter).bi_size && \ ((bvl = bio_iter_mp_iovec((bio), (iter))), 1); \ - bio_advance_mp_iter((bio), &(iter), (bvl).bv_len)) + __bio_advance_iter((bio), &(iter), (bvl).bv_len, 0))
Even we might pass '-1' for multi-page segment.
quoted hunk ↗ jump to hunk
/* returns one real segment(multipage bvec) each time */ #define bio_for_each_bvec(bvl, bio, iter) \diff --git a/include/linux/bvec.h b/include/linux/bvec.h index 02f26d2b59ad..5e2ed46c1c88 100644 --- a/include/linux/bvec.h +++ b/include/linux/bvec.h@@ -138,8 +138,7 @@ struct bvec_iter_all { }) static inline bool __bvec_iter_advance(const struct bio_vec *bv, - struct bvec_iter *iter, - unsigned bytes, bool mp) + struct bvec_iter *iter, unsigned bytes, unsigned max_segment) { if (WARN_ONCE(bytes > iter->bi_size, "Attempted to advance past end of bvec iter\n")) {@@ -148,18 +147,18 @@ static inline bool __bvec_iter_advance(const struct bio_vec *bv, } while (bytes) { - unsigned len; + unsigned segment_len = mp_bvec_iter_len(bv, *iter); - if (mp) - len = mp_bvec_iter_len(bv, *iter); - else - len = bvec_iter_len(bv, *iter); + if (max_segment) { + max_segment -= bvec_iter_offset(bv, *iter); + segment_len = min(segment_len, max_segment);
Looks 'max_segment' needs to be constant, shouldn't be updated. If '-1' is passed for multipage case, the above change may become: segment_len = min_t(segment_len, max_seg_len - bvec_iter_offset(bv, *iter)); This way is more clean, but with extra cost of the above line for multipage case. Thanks, Ming