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>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index d2bbe8cc1e9786b66af798df9d8666d3fb96223c..49e358a0c22f2e17d765626a8dc300cd9e92cfd6 100644 (file)
--- 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)
 {