btrfs: avoid long stall when dropping a non-shared large subvolume

Commit 011b46c30476 ("btrfs: skip subtree scan if it's too high to avoid
low stall in btrfs_commit_transaction()") introduced a mechanism to skip
large subtree during snapshot dropping.

But even for a subvolume without any shared tree blocks, we can still
queue quite a lot of qgroup records into one transaction, and cause a
long qgroup related stall.

So also add a check against the subvolume root level, to determine if we
need to mark qgroup inconsistent.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d6a4390ee34a..a0d5ab03aae2 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -6315,6 +6315,16 @@ int btrfs_drop_snapshot(struct btrfs_root *root, bool update_ref, bool for_reloc
 	set_bit(BTRFS_ROOT_DELETING, &root->state);
 	unfinished_drop = test_bit(BTRFS_ROOT_UNFINISHED_DROP, &root->state);
 
+	/*
+	 * For subvolume dropping, check if the subvolume is large enough so
+	 * that we need to mark qgroup inconsistent to avoid long qgroup stall.
+	 *
+	 * Even for a subvolume without any snapshot, there can still be
+	 * a lot of qgroup records queued into one transaction.
+	 */
+	if (!for_reloc)
+		btrfs_qgroup_check_tree_drop(fs_info, rootid,
+					     btrfs_header_level(root->node));
 	if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
 		level = btrfs_header_level(root->node);
 		path->nodes[level] = btrfs_lock_root_node(root);