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From:   Changheun Lee <nanich.lee@samsung.com>
To:     hch@infradead.org, Johannes.Thumshirn@wdc.com, alex_y_xu@yahoo.ca,
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Cc:     jisoo2146.oh@samsung.com, junho89.kim@samsung.com,
        mj0123.lee@samsung.com, seunghwan.hyun@samsung.com,
        sookwan7.kim@samsung.com, woosung2.lee@samsung.com,
        yt0928.kim@samsung.com, Changheun Lee <nanich.lee@samsung.com>
Subject: [PATCH v11 1/3] bio: control bio max size
Date:   Wed,  2 Jun 2021 21:10:35 +0900
Message-Id: <20210602121037.11083-2-nanich.lee@samsung.com>
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References: <20210602121037.11083-1-nanich.lee@samsung.com>
        <CGME20210602122910epcas1p17ab868175c38cf3f143b64f4ec59f75c@epcas1p1.samsung.com>
Precedence: bulk

bio size can grow up to 4GB after muli-page bvec has been enabled.
But sometimes large size of bio would lead to inefficient behaviors.
Control of bio max size will be helpful to improve inefficiency.

Below is a example for inefficient behaviours.
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>
---
 block/bio.c            | 17 ++++++++++++++---
 block/blk-settings.c   | 19 +++++++++++++++++++
 include/linux/bio.h    |  4 +++-
 include/linux/blkdev.h |  3 +++
 4 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 44205dfb6b60..c52639bb80cd 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.max_bio_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;
 
@@ -1038,6 +1047,7 @@ static int __bio_iov_append_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 request_queue *q = bio->bi_bdev->bd_disk->queue;
 	unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
 	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
@@ -1058,7 +1068,8 @@ static int __bio_iov_append_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 902c40d67120..e270e31519a1 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -32,6 +32,7 @@ EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
  */
 void blk_set_default_limits(struct queue_limits *lim)
 {
+	lim->max_bio_bytes = UINT_MAX;
 	lim->max_segments = BLK_MAX_SEGMENTS;
 	lim->max_discard_segments = 1;
 	lim->max_integrity_segments = 0;
@@ -100,6 +101,24 @@ void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce bounce)
 }
 EXPORT_SYMBOL(blk_queue_bounce_limit);
 
+/**
+ * blk_queue_max_bio_bytes - set bio max size for queue
+ * @q: the request queue for the device
+ * @bytes : bio max bytes to be set
+ *
+ * Description:
+ *    Set proper bio max size to optimize queue operating.
+ **/
+void blk_queue_max_bio_bytes(struct request_queue *q, unsigned int bytes)
+{
+	struct queue_limits *limits = &q->limits;
+	unsigned int max_bio_bytes = round_up(bytes, PAGE_SIZE);
+
+	limits->max_bio_bytes = max_t(unsigned int, max_bio_bytes,
+				      BIO_MAX_VECS * PAGE_SIZE);
+}
+EXPORT_SYMBOL(blk_queue_max_bio_bytes);
+
 /**
  * blk_queue_max_hw_sectors - set max sectors for a request for this queue
  * @q:  the request queue for the device
diff --git a/include/linux/bio.h b/include/linux/bio.h
index a0b4cfdf62a4..f1a99f0a240c 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -106,6 +106,8 @@ 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
@@ -119,7 +121,7 @@ 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 1255823b2bc0..861888501fc0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -326,6 +326,8 @@ enum blk_bounce {
 };
 
 struct queue_limits {
+	unsigned int		max_bio_bytes;
+
 	enum blk_bounce		bounce;
 	unsigned long		seg_boundary_mask;
 	unsigned long		virt_boundary_mask;
@@ -1132,6 +1134,7 @@ extern void blk_abort_request(struct request *);
  * Access functions for manipulating queue properties
  */
 extern void blk_cleanup_queue(struct request_queue *);
+extern void blk_queue_max_bio_bytes(struct request_queue *, unsigned int);
 void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce limit);
 extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
 extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
-- 
2.29.0