In case of big chunk sequential IO, bio size is often not aligned with queue's max IO size because of multipage bvec, and unaligned & small bio can be caused by bio split, then sequential IO perf drops, so try to align bio with max IO size for avoiding this issue. Provide 'max_size' hint to iov_iter_extract_pages() when this bio is close to be full, and try to keep bio aligned with max IO size, so that we can minimize bio & iov_iter revert. In my 1GB IO test over VM with 2G ram, when memory becomes highly fragmented, revert ratio(revert bytes/buf size) can be kept as small as 0.5% with this algorithm. Ed Tsai reported that this change improves 64MB read/write by > 15%~25% in Antutu V10 Storage Test. Reported-by: Ed Tsai <ed.tsai@xxxxxxxxxxxx> Closes: https://lore.kernel.org/linux-block/20231025092255.27930-1-ed.tsai@xxxxxxxxxxxx/ Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- block/bio.c | 116 +++++++++++++++++++++++++++++++++++++++-- include/linux/blkdev.h | 5 ++ 2 files changed, 118 insertions(+), 3 deletions(-) diff --git a/block/bio.c b/block/bio.c index 09a5e71a0372..e360ac052764 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1210,6 +1210,57 @@ static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page, return 0; } +/* + * Figure out max_size hint of iov_iter_extract_pages() for minimizing + * bio & iov iter revert so that bio can be aligned with max io size. + */ +static unsigned int bio_get_buffer_size_hint(const struct bio *bio, + unsigned int left) +{ + unsigned int nr_bvecs = bio->bi_max_vecs - bio->bi_vcnt; + unsigned int size, predicted_space, max_bytes; + unsigned int space = nr_bvecs << PAGE_SHIFT; + unsigned int align_deviation; + + /* If we have enough space really, just try to get all pages */ + if (!bio->bi_bdev || nr_bvecs >= (bio->bi_max_vecs / 4) || + !bio->bi_vcnt || left <= space) + return UINT_MAX - size; + + max_bytes = bdev_max_io_bytes(bio->bi_bdev); + size = bio->bi_iter.bi_size; + + /* + * One bvec can hold physically continuous page frames with + * multipage bvec and bytes in these pages can be pretty big, so + * predict the available space by averaging bytes on all bvecs + */ + predicted_space = size * nr_bvecs / bio->bi_vcnt; + /* + * If predicted space is bigger than max io bytes and at least two + * vectors left, ask for all pages + */ + if (predicted_space > max_bytes && nr_bvecs > 2) + return UINT_MAX - size; + + /* + * This bio is close to be full, and stop to add pages if it is + * basically aligned, otherwise just get & add pages if the bio + * can be kept as aligned, so that we can minimize bio & iov iter + * revert + */ + align_deviation = max_t(unsigned int, 16U * 1024, max_bytes / 16); + if ((size & (max_bytes - 1)) > align_deviation) { + unsigned aligned_bytes = max_bytes - (size & (max_bytes - 1)); + + /* try to keep bio aligned if we have enough data and space */ + if (aligned_bytes <= left && aligned_bytes <= predicted_space) + return aligned_bytes; + } + + return 0; +} + #define PAGE_PTRS_PER_BVEC (sizeof(struct bio_vec) / sizeof(struct page *)) /** @@ -1229,7 +1280,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; struct page **pages = (struct page **)bv; - ssize_t size, left; + ssize_t size, left, max_size; unsigned len, i = 0; size_t offset; int ret = 0; @@ -1245,6 +1296,10 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) if (bio->bi_bdev && blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue)) extraction_flags |= ITER_ALLOW_P2PDMA; + max_size = bio_get_buffer_size_hint(bio, iov_iter_count(iter)); + if (!max_size) + return -E2BIG; + /* * Each segment in the iov is required to be a block size multiple. * However, we may not be able to get the entire segment if it spans @@ -1252,8 +1307,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) * result to ensure the bio's total size is correct. The remainder of * the iov data will be picked up in the next bio iteration. */ - size = iov_iter_extract_pages(iter, &pages, - UINT_MAX - bio->bi_iter.bi_size, + size = iov_iter_extract_pages(iter, &pages, max_size, nr_pages, extraction_flags, &offset); if (unlikely(size <= 0)) return size ? size : -EFAULT; @@ -1298,6 +1352,46 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) return ret; } +/* should only be called before submission */ +static void bio_shrink(struct bio *bio, unsigned bytes) +{ + unsigned int size = bio->bi_iter.bi_size; + int idx; + + if (bytes >= size) + return; + + WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)); + + idx = bio->bi_vcnt - 1; + bio->bi_iter.bi_size -= bytes; + while (bytes > 0) { + struct bio_vec *bv = &bio->bi_io_vec[idx]; + unsigned int len = min_t(unsigned, bv->bv_len, bytes); + + bytes -= len; + bv->bv_len -= len; + if (!bv->bv_len) { + bio_release_page(bio, bv->bv_page); + idx--; + } + } + WARN_ON_ONCE(idx < 0); + bio->bi_vcnt = idx + 1; +} + +static unsigned bio_align_with_io_size(struct bio *bio) +{ + unsigned int size = bio->bi_iter.bi_size; + unsigned int trim = size & (bdev_max_io_bytes(bio->bi_bdev) - 1); + + if (trim && trim != size) { + bio_shrink(bio, trim); + return trim; + } + return 0; +} + /** * bio_iov_iter_get_pages - add user or kernel pages to a bio * @bio: bio to add pages to @@ -1337,6 +1431,22 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) ret = __bio_iov_iter_get_pages(bio, iter); } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0)); + + /* + * If we still have data and bio is full, this bio size may not be + * aligned with max io size, small bio can be caused by split, try + * to avoid this situation by aligning bio with max io size. + * + * Big chunk of sequential IO workload can benefit from this way. + */ + if (!ret && iov_iter_count(iter) && bio->bi_bdev && + bio_op(bio) != REQ_OP_ZONE_APPEND) { + unsigned trim = bio_align_with_io_size(bio); + + if (trim) + iov_iter_revert(iter, trim); + } + return bio->bi_vcnt ? 0 : ret; } EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index eef450f25982..2d275cdc39d8 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1151,6 +1151,11 @@ static inline unsigned queue_logical_block_size(const struct request_queue *q) return retval; } +static inline unsigned int bdev_max_io_bytes(struct block_device *bdev) +{ + return queue_max_bytes(bdev_get_queue(bdev)); +} + static inline unsigned int bdev_logical_block_size(struct block_device *bdev) { return queue_logical_block_size(bdev_get_queue(bdev)); -- 2.41.0
