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authorChangheun Lee <nanich.lee@samsung.com>2021-05-03 18:52:03 +0900
committerJens Axboe <axboe@kernel.dk>2021-05-03 11:00:11 -0600
commitcd2c7545ae1beac3b6aae033c7f31193b3255946 (patch)
treea11a36fec261988bca89d3b3d9241d13fa48ce79 /block
parentc646790a1fcae7738972accc41ccaa4983e5c234 (diff)
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 <nanich.lee@samsung.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Link: https://lore.kernel.org/r/20210503095203.29076-1-nanich.lee@samsung.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/bio.c13
-rw-r--r--block/blk-settings.c5
2 files changed, 16 insertions, 2 deletions
diff --git a/block/bio.c b/block/bio.c
index 44205dfb6b60..221dc56ba22f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -255,6 +255,13 @@ void bio_init(struct bio *bio, struct bio_vec *table,
}
EXPORT_SYMBOL(bio_init);
+unsigned int bio_max_size(struct bio *bio)
+{
+ struct block_device *bdev = bio->bi_bdev;
+
+ return bdev ? bdev->bd_disk->queue->limits.bio_max_bytes : UINT_MAX;
+}
+
/**
* bio_reset - reinitialize a bio
* @bio: bio to reset
@@ -866,7 +873,7 @@ 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;
}
@@ -995,6 +1002,7 @@ 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;
@@ -1010,7 +1018,8 @@ 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 9c009090c4b5..c646503e55d2 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -31,6 +31,7 @@ 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;
@@ -139,6 +140,10 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
limits->logical_block_size >> SECTOR_SHIFT);
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);

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