Btrfs: unplug every once and a while

The btrfs io submission threads can build up massive plug lists.  This
keeps things more reasonable so we don't hand over huge dumps of IO at
once.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 91ea57a1474a..f4b839fd3c9d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -295,6 +295,12 @@ loop_lock:
                         btrfs_requeue_work(&device->work);
                         goto done;
                 }
+                /* unplug every 64 requests just for good measure */
+                if (batch_run % 64 == 0) {
+                        blk_finish_plug(&plug);
+                        blk_start_plug(&plug);
+                        sync_pending = 0;
+                }
         }
 
         cond_resched();