Btrfs: Metadata ENOSPC handling for balance

This patch adds metadata ENOSPC handling for the balance code.
It is consisted by following major changes:

1. Avoid COW tree leave in the phrase of merging tree.

2. Handle interaction with snapshot creation.

3. make the backref cache can live across transactions.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 6bee8e5204fb..acd532af8e55 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -447,6 +447,9 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
 
         update_ref_for_cow(trans, root, buf, cow, &last_ref);
 
+        if (root->ref_cows)
+                btrfs_reloc_cow_block(trans, root, buf, cow);
+
         if (buf == root->node) {
                 WARN_ON(parent && parent != buf);
                 if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||