Btrfs: Throttle operations if the reference cache gets too large

A large reference cache is directly related to a lot of work pending
for the cleaner thread.  This throttles back new operations based on
the size of the reference cache so the cleaner thread will be able to keep
up.

Overall, this actually makes the FS faster because the cleaner thread will
be more likely to find things in cache.

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 4eca0aa1ce74..5517dfc6f71c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -580,6 +580,7 @@ struct btrfs_fs_info {
         int do_barriers;
         int closing;
         atomic_t throttles;
+        atomic_t throttle_gen;
 
         u64 total_pinned;
         struct list_head dirty_cowonly_roots;