btrfs: scrub: add explicit plugging

With the removal of the implicit plugging scrub ends up doing more and
smaller I/O than necessary. This patch adds explicit plugging per chunk.

Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 2d1f8909a8e1..1204eab94028 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -348,9 +348,6 @@ static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
         int ret;
         DECLARE_COMPLETION_ONSTACK(complete);
 
-        /* we are going to wait on this IO */
-        rw |= REQ_SYNC;
-
         bio = bio_alloc(GFP_NOFS, 1);
         bio->bi_bdev = bdev;
         bio->bi_sector = sector;
@@ -359,6 +356,7 @@ static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
         bio->bi_private = &complete;
         submit_bio(rw, bio);
 
+        /* this will also unplug the queue */
         wait_for_completion(&complete);
 
         ret = !test_bit(BIO_UPTODATE, &bio->bi_flags);
@@ -743,6 +741,7 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
         struct btrfs_root *root = fs_info->extent_root;
         struct btrfs_root *csum_root = fs_info->csum_root;
         struct btrfs_extent_item *extent;
+        struct blk_plug plug;
         u64 flags;
         int ret;
         int slot;
@@ -847,6 +846,7 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
          * the scrub. This might currently (crc32) end up to be about 1MB
          */
         start_stripe = 0;
+        blk_start_plug(&plug);
 again:
         logical = base + offset + start_stripe * increment;
         for (i = start_stripe; i < nstripes; ++i) {
@@ -988,6 +988,7 @@ next:
         scrub_submit(sdev);
 
 out:
+        blk_finish_plug(&plug);
         btrfs_free_path(path);
         return ret < 0 ? ret : 0;
 }