Btrfs: process the delayed reference queue in clusters

The delayed reference queue maintains pending operations that need to
be done to the extent allocation tree.  These are processed by
finding records in the tree that are not currently being processed one at
a time.

This is slow because it uses lots of time searching through the rbtree
and because it creates lock contention on the extent allocation tree
when lots of different procs are running delayed refs at the same time.

This commit changes things to grab a cluster of refs for processing,
using a cursor into the rbtree as the starting point of the next search.
This way we walk smoothly through the rbtree.

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 ced5fd85dc36..08d9f8d15538 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -720,6 +720,7 @@ struct btrfs_fs_info {
         struct mutex drop_mutex;
         struct mutex volume_mutex;
         struct mutex tree_reloc_mutex;
+
         struct list_head trans_list;
         struct list_head hashers;
         struct list_head dead_roots;