From 9458fa0dda6eab9c53cd0dcc882f69793513ddd2 Mon Sep 17 00:00:00 2001 From: Changheun Lee Date: Mon, 3 May 2021 18:52:03 +0900 Subject: [PATCH] BACKPORT: bio: limit bio max size bio size can grow up to 4GB when muli-page bvec is enabled. but sometimes it would lead to inefficient behaviors. in case of large chunk direct I/O, - 32MB chunk read in user space - all pages for 32MB would be merged to a bio structure if the pages physical addresses are contiguous. it makes some delay to submit until merge complete. bio max size should be limited to a proper size. When 32MB chunk read with direct I/O option is coming from userspace, kernel behavior is below now in do_direct_IO() loop. it's timeline. | bio merge for 32MB. total 8,192 pages are merged. | total elapsed time is over 2ms. |------------------ ... ----------------------->| | 8,192 pages merged a bio. | at this time, first bio submit is done. | 1 bio is split to 32 read request and issue. |---------------> |---------------> |---------------> ...... |---------------> |--------------->| total 19ms elapsed to complete 32MB read done from device. | If bio max size is limited with 1MB, behavior is changed below. | bio merge for 1MB. 256 pages are merged for each bio. | total 32 bio will be made. | total elapsed time is over 2ms. it's same. | but, first bio submit timing is fast. about 100us. |--->|--->|--->|---> ... -->|--->|--->|--->|--->| | 256 pages merged a bio. | at this time, first bio submit is done. | and 1 read request is issued for 1 bio. |---------------> |---------------> |---------------> ...... |---------------> |--------------->| total 17ms elapsed to complete 32MB read done from device. | As a result, read request issue timing is faster if bio max size is limited. Current kernel behavior with multipage bvec, super large bio can be created. And it lead to delay first I/O request issue. Signed-off-by: Changheun Lee Reviewed-by: Bart Van Assche Link: https://lore.kernel.org/r/20210503095203.29076-1-nanich.lee@samsung.com Signed-off-by: Jens Axboe Bug: 182716953 (cherry picked from commit cd2c7545ae1beac3b6aae033c7f31193b3255946) Change-Id: Ie3876daa495535dc7f856ed9a281e65d72a437c1 Signed-off-by: Bart Van Assche --- block/bio.c | 15 +++++++++++++-- block/blk-settings.c | 6 ++++++ include/linux/bio.h | 4 +++- include/linux/blkdev.h | 2 ++ 4 files changed, 24 insertions(+), 3 deletions(-) diff --git a/block/bio.c b/block/bio.c index 9c931df2d986..9620daf1d7b8 100644 --- a/block/bio.c +++ b/block/bio.c @@ -287,6 +287,15 @@ void bio_init(struct bio *bio, struct bio_vec *table, } EXPORT_SYMBOL(bio_init); +unsigned int bio_max_size(struct bio *bio) +{ + struct gendisk *disk = bio->bi_disk; + + /* bio_map_kern() allocates a bio but does not set bio->bi_disk. */ + return disk ? disk->queue->limits.bio_max_bytes : UINT_MAX; +} +EXPORT_SYMBOL(bio_max_size); + /** * bio_reset - reinitialize a bio * @bio: bio to reset @@ -877,7 +886,7 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page, struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1]; if (page_is_mergeable(bv, page, len, off, same_page)) { - if (bio->bi_iter.bi_size > UINT_MAX - len) { + if (bio->bi_iter.bi_size > bio_max_size(bio) - len) { *same_page = false; return false; } @@ -994,6 +1003,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) { unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt; unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; + unsigned int bytes_left = bio_max_size(bio) - bio->bi_iter.bi_size; struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; struct page **pages = (struct page **)bv; bool same_page = false; @@ -1009,7 +1019,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2); pages += entries_left * (PAGE_PTRS_PER_BVEC - 1); - size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); + size = iov_iter_get_pages(iter, pages, bytes_left, nr_pages, + &offset); if (unlikely(size <= 0)) return size ? size : -EFAULT; diff --git a/block/blk-settings.c b/block/blk-settings.c index c3aa7f8ee388..5140f62202dc 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -37,6 +37,7 @@ EXPORT_SYMBOL_GPL(blk_queue_rq_timeout); */ void blk_set_default_limits(struct queue_limits *lim) { + lim->bio_max_bytes = UINT_MAX; lim->max_segments = BLK_MAX_SEGMENTS; lim->max_discard_segments = 1; lim->max_integrity_segments = 0; @@ -161,6 +162,11 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors); max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS); limits->max_sectors = max_sectors; + + if (check_shl_overflow(max_sectors, SECTOR_SHIFT, + &limits->bio_max_bytes)) + limits->bio_max_bytes = UINT_MAX; + q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9); } EXPORT_SYMBOL(blk_queue_max_hw_sectors); diff --git a/include/linux/bio.h b/include/linux/bio.h index c6d765382926..243c0f8eca38 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -100,6 +100,8 @@ static inline void *bio_data(struct bio *bio) return NULL; } +extern unsigned int bio_max_size(struct bio *bio); + /** * bio_full - check if the bio is full * @bio: bio to check @@ -113,7 +115,7 @@ static inline bool bio_full(struct bio *bio, unsigned len) if (bio->bi_vcnt >= bio->bi_max_vecs) return true; - if (bio->bi_iter.bi_size > UINT_MAX - len) + if (bio->bi_iter.bi_size > bio_max_size(bio) - len) return true; return false; diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 668e6a732025..e30acaed8f86 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -316,6 +316,8 @@ enum blk_zoned_model { }; struct queue_limits { + unsigned int bio_max_bytes; + unsigned long bounce_pfn; unsigned long seg_boundary_mask; unsigned long virt_boundary_mask;