dm thin: optimize async discard submission

__blkdev_issue_discard_async() doesn't need to worry about further
splitting because the upper layer blkdev_issue_discard() will have
already handled splitting bios such that the bi_size isn't
overflowed.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>

1 files changed, 15 insertions, 74 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index d2bbe8cc1e97..49e358a0c22f 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -332,9 +332,6 @@ struct thin_c {
  *
  * Description:
  *    Asynchronously issue a discard request for the sectors in question.
- *    NOTE: this variant of blk-core's blkdev_issue_discard() is a stop-gap
- *    that is being kept local to DM thinp until the block changes to allow
- *    late bio splitting land upstream.
  */
 static int __blkdev_issue_discard_async(struct block_device *bdev, sector_t sector,
                                         sector_t nr_sects, gfp_t gfp_mask, unsigned long flags,
@@ -342,91 +339,36 @@ static int __blkdev_issue_discard_async(struct block_device *bdev, sector_t sect
 {
         struct request_queue *q = bdev_get_queue(bdev);
         int type = REQ_WRITE | REQ_DISCARD;
-        unsigned int max_discard_sectors, granularity;
-        int alignment;
         struct bio *bio;
-        int ret = 0;
-        struct blk_plug plug;
 
-        if (!q)
+        if (!q || !nr_sects)
                 return -ENXIO;
 
         if (!blk_queue_discard(q))
                 return -EOPNOTSUPP;
 
-        /* Zero-sector (unknown) and one-sector granularities are the same.  */
-        granularity = max(q->limits.discard_granularity >> 9, 1U);
-        alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
-
-        /*
-         * Ensure that max_discard_sectors is of the proper
-         * granularity, so that requests stay aligned after a split.
-         */
-        max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
-        max_discard_sectors -= max_discard_sectors % granularity;
-        if (unlikely(!max_discard_sectors)) {
-                /* Avoid infinite loop below. Being cautious never hurts. */
-                return -EOPNOTSUPP;
-        }
-
         if (flags & BLKDEV_DISCARD_SECURE) {
                 if (!blk_queue_secdiscard(q))
                         return -EOPNOTSUPP;
                 type |= REQ_SECURE;
         }
 
-        blk_start_plug(&plug);
-        while (nr_sects) {
-                unsigned int req_sects;
-                sector_t end_sect, tmp;
-
-                /*
-                 * Required bio_put occurs in bio_endio thanks to bio_chain below
-                 */
-                bio = bio_alloc(gfp_mask, 1);
-                if (!bio) {
-                        ret = -ENOMEM;
-                        break;
-                }
-
-                req_sects = min_t(sector_t, nr_sects, max_discard_sectors);
-
-                /*
-                 * If splitting a request, and the next starting sector would be
-                 * misaligned, stop the discard at the previous aligned sector.
-                 */
-                end_sect = sector + req_sects;
-                tmp = end_sect;
-                if (req_sects < nr_sects &&
-                    sector_div(tmp, granularity) != alignment) {
-                        end_sect = end_sect - alignment;
-                        sector_div(end_sect, granularity);
-                        end_sect = end_sect * granularity + alignment;
-                        req_sects = end_sect - sector;
-                }
-
-                bio_chain(bio, parent_bio);
-
-                bio->bi_iter.bi_sector = sector;
-                bio->bi_bdev = bdev;
+        /*
+         * Required bio_put occurs in bio_endio thanks to bio_chain below
+         */
+        bio = bio_alloc(gfp_mask, 1);
+        if (!bio)
+                return -ENOMEM;
 
-                bio->bi_iter.bi_size = req_sects << 9;
-                nr_sects -= req_sects;
-                sector = end_sect;
+        bio_chain(bio, parent_bio);
 
-                submit_bio(type, bio);
+        bio->bi_iter.bi_sector = sector;
+        bio->bi_bdev = bdev;
+        bio->bi_iter.bi_size = nr_sects << 9;
 
-                /*
-                 * We can loop for a long time in here, if someone does
-                 * full device discards (like mkfs). Be nice and allow
-                 * us to schedule out to avoid softlocking if preempt
-                 * is disabled.
-                 */
-                cond_resched();
-        }
-        blk_finish_plug(&plug);
+        submit_bio(type, bio);
 
-        return ret;
+        return 0;
 }
 
 static bool block_size_is_power_of_two(struct pool *pool)
@@ -1539,9 +1481,8 @@ static void process_discard_cell_no_passdown(struct thin_c *tc,
 }
 
 /*
- * FIXME: DM local hack to defer parent bios's end_io until we
- * _know_ all chained sub range discard bios have completed.
- * Will go away once late bio splitting lands upstream!
+ * __bio_inc_remaining() is used to defer parent bios's end_io until
+ * we _know_ all chained sub range discard bios have completed.
  */
 static inline void __bio_inc_remaining(struct bio *bio)
 {