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, 9 insertions, 14 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a713f69f0c7a..d61a799fe323 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5875,7 +5875,8 @@ static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
  * also make sure backrefs for the shared block and all lower level
  * blocks are properly updated.
  */
-int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref)
+int btrfs_drop_snapshot(struct btrfs_root *root,
+                        struct btrfs_block_rsv *block_rsv, int update_ref)
 {
         struct btrfs_path *path;
         struct btrfs_trans_handle *trans;
@@ -5894,6 +5895,8 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref)
         BUG_ON(!wc);
 
         trans = btrfs_start_transaction(tree_root, 0);
+        if (block_rsv)
+                trans->block_rsv = block_rsv;
 
         if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
                 level = btrfs_header_level(root->node);
@@ -5981,24 +5984,16 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref)
                 }
 
                 BUG_ON(wc->level == 0);
-                if (trans->transaction->in_commit ||
-                    trans->transaction->delayed_refs.flushing) {
+                if (btrfs_should_end_transaction(trans, tree_root)) {
                         ret = btrfs_update_root(trans, tree_root,
                                                 &root->root_key,
                                                 root_item);
                         BUG_ON(ret);
 
-                        btrfs_end_transaction(trans, tree_root);
+                        btrfs_end_transaction_throttle(trans, tree_root);
                         trans = btrfs_start_transaction(tree_root, 0);
-                        if (IS_ERR(trans))
-                                return PTR_ERR(trans);
-                } else {
-                        unsigned long update;
-                        update = trans->delayed_ref_updates;
-                        trans->delayed_ref_updates = 0;
-                        if (update)
-                                btrfs_run_delayed_refs(trans, tree_root,
-                                                       update);
+                        if (block_rsv)
+                                trans->block_rsv = block_rsv;
                 }
         }
         btrfs_release_path(root, path);
@@ -6026,7 +6021,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref)
                 kfree(root);
         }
 out:
-        btrfs_end_transaction(trans, tree_root);
+        btrfs_end_transaction_throttle(trans, tree_root);
         kfree(wc);
         btrfs_free_path(path);
         return err;