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 memory address is continued phsycally. it makes some delay to submit until merge complete. bio max size should be limited as a proper size.
When 32MB chunk read with direct I/O option is coming from userspace, kernel behavior is below now. 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 <nanich....@samsung.com> --- block/bio.c | 17 ++++++++++++++++- include/linux/bio.h | 13 +++---------- include/linux/blk_types.h | 1 + 3 files changed, 20 insertions(+), 11 deletions(-) diff --git a/block/bio.c b/block/bio.c index 1f2cc1fbe283..027503c2e2e7 100644 --- a/block/bio.c +++ b/block/bio.c @@ -284,9 +284,24 @@ void bio_init(struct bio *bio, struct bio_vec *table, bio->bi_io_vec = table; bio->bi_max_vecs = max_vecs; + bio->bi_max_size = UINT_MAX; } EXPORT_SYMBOL(bio_init); +void bio_set_dev(struct bio *bio, struct block_device *bdev) +{ + if (bio->bi_disk != bdev->bd_disk) + bio_clear_flag(bio, BIO_THROTTLED); + + bio->bi_disk = bdev->bd_disk; + bio->bi_partno = bdev->bd_partno; + bio->bi_max_size = blk_queue_get_max_sectors(bio->bi_disk->queue, + bio_op(bio)) << SECTOR_SHIFT; + + bio_associate_blkg(bio); +} +EXPORT_SYMBOL(bio_set_dev); + /** * bio_reset - reinitialize a bio * @bio: bio to reset @@ -877,7 +892,7 @@ 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->bi_max_size - len) *same_page = false; return false; } diff --git a/include/linux/bio.h b/include/linux/bio.h index 1edda614f7ce..b9803e80c259 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -113,7 +113,7 @@ 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->bi_max_size - len) return true; return false; @@ -482,20 +482,13 @@ extern struct bio_vec *bvec_alloc(gfp_t, int, unsigned long *, mempool_t *); extern void bvec_free(mempool_t *, struct bio_vec *, unsigned int); extern unsigned int bvec_nr_vecs(unsigned short idx); extern const char *bio_devname(struct bio *bio, char *buffer); - -#define bio_set_dev(bio, bdev) \ -do { \ - if ((bio)->bi_disk != (bdev)->bd_disk) \ - bio_clear_flag(bio, BIO_THROTTLED);\ - (bio)->bi_disk = (bdev)->bd_disk; \ - (bio)->bi_partno = (bdev)->bd_partno; \ - bio_associate_blkg(bio); \ -} while (0) +extern void bio_set_dev(struct bio *bio, struct block_device *bdev); #define bio_copy_dev(dst, src) \ do { \ (dst)->bi_disk = (src)->bi_disk; \ (dst)->bi_partno = (src)->bi_partno; \ + (dst)->bi_max_size = (src)->bi_max_size;\ bio_clone_blkg_association(dst, src); \ } while (0) diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 866f74261b3b..e5dd5b7d8fc1 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -270,6 +270,7 @@ struct bio { */ unsigned short bi_max_vecs; /* max bvl_vecs we can hold */ + unsigned int bi_max_size; /* max data size we can hold */ atomic_t __bi_cnt; /* pin count */ -- 2.28.0