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.lee@xxxxxxxxxxx>
---
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
