[RFC,v3] block: avoid the unnecessary blk_bio_discard_split()

Commit Message

Tom Yan Dec. 11, 2020, 4:13 p.m. UTC

It doesn't seem necessary to have the redundant layer of splitting.
The request size will even be more consistent / aligned to the cap.

Signed-off-by: Tom Yan <[e-mail]>
---
 block/blk-lib.c   | 11 +++++++++--
 block/blk-merge.c |  2 +-
 block/blk.h       |  8 ++++++--
 3 files changed, 16 insertions(+), 5 deletions(-)

Comments

Chaitanya Kulkarni Dec. 12, 2020, 2:01 a.m. UTC | #1

On 12/11/20 08:17, Tom Yan wrote:
> It doesn't seem necessary to have the redundant layer of splitting.
> The request size will even be more consistent / aligned to the cap.
>
> Signed-off-by: Tom Yan <[e-mail]>
Can you please explain why the change log is missing ?

Patch

diff --git a/block/blk-lib.c b/block/blk-lib.c
index e90614fd8d6a..cbf55c9f0d6f 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -85,12 +85,19 @@  int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 		 *   is split in device drive, the split ones are very probably
 		 *   to be aligned to discard_granularity of the device's queue.
 		 */
-		if (granularity_aligned_lba == sector_mapped)
+		if (granularity_aligned_lba == sector_mapped) {
 			req_sects = min_t(sector_t, nr_sects,
 					  bio_aligned_discard_max_sectors(q));
-		else
+			if (!req_sects)
+				return -EOPNOTSUPP;
+		} else {
 			req_sects = min_t(sector_t, nr_sects,
 					  granularity_aligned_lba - sector_mapped);
+		}
+
+		/* Zero-sector (unknown) and one-sector granularities are the same.  */
+		granularity = max(q->limits.discard_granularity >> SECTOR_SHIFT, 1U);
+		req_sects = round_down(req_sects, granularity);
 
 		WARN_ON_ONCE((req_sects << 9) > UINT_MAX);
 
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 97b7c2821565..f4e030fe6399 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -59,6 +59,7 @@  static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
 	return bio_will_gap(req->q, NULL, bio, req->bio);
 }
 
+/* deprecated */
 static struct bio *blk_bio_discard_split(struct request_queue *q,
 					 struct bio *bio,
 					 struct bio_set *bs,
@@ -303,7 +304,6 @@  void __blk_queue_split(struct bio **bio, unsigned int *nr_segs)
 	switch (bio_op(*bio)) {
 	case REQ_OP_DISCARD:
 	case REQ_OP_SECURE_ERASE:
-		split = blk_bio_discard_split(q, *bio, &q->bio_split, nr_segs);
 		break;
 	case REQ_OP_WRITE_ZEROES:
 		split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split,
diff --git a/block/blk.h b/block/blk.h
index dfab98465db9..508371fafdf3 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -281,8 +281,12 @@  static inline unsigned int bio_allowed_max_sectors(struct request_queue *q)
 static inline unsigned int bio_aligned_discard_max_sectors(
 					struct request_queue *q)
 {
-	return round_down(UINT_MAX, q->limits.discard_granularity) >>
-			SECTOR_SHIFT;
+	unsigned int discard_max_sectors, granularity;
+	discard_max_sectors = min(q->limits.max_discard_sectors,
+				  bio_allowed_max_sectors(q));
+	/* Zero-sector (unknown) and one-sector granularities are the same.  */
+	granularity = max(q->limits.discard_granularity >> SECTOR_SHIFT, 1U);
+	return round_down(discard_max_sectors, granularity);
 }
 
 /*