Btrfs: Wait for kernel threads to make progress during async submission

Before this change, btrfs would use a bdi congestion function to make
sure there weren't too many pending async checksum work items.

This change makes the process creating async work items wait instead,
leading to fewer congestion returns from the bdi.  This improves
pdflush background_writeout scanning.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index bb4a8d2200d..04021335939 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -526,6 +526,7 @@ struct btrfs_fs_info {
         struct btrfs_transaction *running_transaction;
         wait_queue_head_t transaction_throttle;
         wait_queue_head_t transaction_wait;
+        wait_queue_head_t async_submit_wait;
         struct btrfs_super_block super_copy;
         struct btrfs_super_block super_for_commit;
         struct block_device *__bdev;