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>

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 2d1f8909a8e16231457673d7a8ddf723daa315f5..1204eab94028db2adae4479ec96623fb0ac8b854 100644 (file)
--- 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;
 }