[PATCH 22/27] block: refactor discard bio size limiting

Christoph Hellwig
2022-04-15T05:02:41Z

Move all the logic to limit the discard bio size into a common helper
so that it is better documented.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Coly Li <colyli@suse.de>
---
block/blk-lib.c | 59 ++++++++++++++++++++++++-------------------------
block/blk.h | 14 ------------
2 files changed, 29 insertions(+), 44 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 237d60d8b5857..2ae32a722851c 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -10,6 +10,32 @@

#include "blk.h"

+static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
+{
+ unsigned int discard_granularity =
+ bdev_get_queue(bdev)->limits.discard_granularity;
+ sector_t granularity_aligned_sector;
+
+ if (bdev_is_partition(bdev))
+ sector += bdev->bd_start_sect;
+
+ granularity_aligned_sector =
+ round_up(sector, discard_granularity >> SECTOR_SHIFT);
+
+ /*
+ * Make sure subsequent bios start aligned to the discard granularity if
+ * it needs to be split.
+ */
+ if (granularity_aligned_sector != sector)
+ return granularity_aligned_sector - sector;
+
+ /*
+ * Align the bio size to the discard granularity to make splitting the bio
+ * at discard granularity boundaries easier in the driver if needed.
+ */
+ return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
+}
+
int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
sector_t nr_sects, gfp_t gfp_mask, int flags,
struct bio **biop)
@@ -17,7 +43,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
struct request_queue *q = bdev_get_queue(bdev);
struct bio *bio = *biop;
unsigned int op;
- sector_t bs_mask, part_offset = 0;
+ sector_t bs_mask;

if (bdev_read_only(bdev))
return -EPERM;
@@ -48,36 +74,9 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
if (!nr_sects)
return -EINVAL;

- /* In case the discard request is in a partition */
- if (bdev_is_partition(bdev))
- part_offset = bdev->bd_start_sect;
-
while (nr_sects) {
- sector_t granularity_aligned_lba, req_sects;
- sector_t sector_mapped = sector + part_offset;
-
- granularity_aligned_lba = round_up(sector_mapped,
- q->limits.discard_granularity >> SECTOR_SHIFT);
-
- /*
- * Check whether the discard bio starts at a discard_granularity
- * aligned LBA,
- * - If no: set (granularity_aligned_lba - sector_mapped) to
- * bi_size of the first split bio, then the second bio will
- * start at a discard_granularity aligned LBA on the device.
- * - If yes: use bio_aligned_discard_max_sectors() as the max
- * possible bi_size of the first split bio. Then when this bio
- * 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)
- req_sects = min_t(sector_t, nr_sects,
- bio_aligned_discard_max_sectors(q));
- else
- req_sects = min_t(sector_t, nr_sects,
- granularity_aligned_lba - sector_mapped);
-
- WARN_ON_ONCE((req_sects << 9) > UINT_MAX);
+ sector_t req_sects =
+ min(nr_sects, bio_discard_limit(bdev, sector));

bio = blk_next_bio(bio, bdev, 0, op, gfp_mask);
bio->bi_iter.bi_sector = sector;
diff --git a/block/blk.h b/block/blk.h
index 4ea5167dc3392..434017701403f 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -346,20 +346,6 @@ static inline unsigned int bio_allowed_max_sectors(struct request_queue *q)
return round_down(UINT_MAX, queue_logical_block_size(q)) >> 9;
}

-/*
- * The max bio size which is aligned to q->limits.discard_granularity. This
- * is a hint to split large discard bio in generic block layer, then if device
- * driver needs to split the discard bio into smaller ones, their bi_size can
- * be very probably and easily aligned to discard_granularity of the device's
- * queue.
- */
-static inline unsigned int bio_aligned_discard_max_sectors(
- struct request_queue *q)
-{
- return round_down(UINT_MAX, q->limits.discard_granularity) >>
- SECTOR_SHIFT;
-}
-
/*
* Internal io_context interface
*/