diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4dd478b4fe3a..891f47c7891f 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1162,6 +1162,7 @@ struct btrfs_root {
 	spinlock_t qgroup_meta_rsv_lock;
 	u64 qgroup_meta_rsv_pertrans;
 	u64 qgroup_meta_rsv_prealloc;
+	struct mutex qgroup_flushing_mutex;
 
 	/* Number of active swapfiles */
 	atomic_t nr_swapfiles;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7c07578866f3..ca2c7d39e9f7 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1116,6 +1116,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
 	mutex_init(&root->log_mutex);
 	mutex_init(&root->ordered_extent_mutex);
 	mutex_init(&root->delalloc_mutex);
+	mutex_init(&root->qgroup_flushing_mutex);
 	init_waitqueue_head(&root->log_writer_wait);
 	init_waitqueue_head(&root->log_commit_wait[0]);
 	init_waitqueue_head(&root->log_commit_wait[1]);
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 5cfd2bcc55ef..24b4aed57249 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3508,20 +3508,62 @@ static void qgroup_revert(struct btrfs_inode *inode,
 }
 
 /*
- * Reserve qgroup space for range [start, start + len).
+ * Try to free some space for qgroup.
  *
- * This function will either reserve space from related qgroups or doing
- * nothing if the range is already reserved.
+ * For qgroup, there are only 3 ways to free qgroup space:
+ * - Flush nodatacow write
+ *   Any nodatacow write will free its reserved data space at
+ *   run_delalloc_range().
+ *   In theory, we should only flush nodatacow inodes, but it's
+ *   not yet possible, so we need to flush the whole root.
  *
- * Return 0 for successful reserve
- * Return <0 for error (including -EQUOT)
+ * - Wait for ordered extents
+ *   When ordered extents are finished, their reserved metadata
+ *   is finally converted to per_trans status, which can be freed
+ *   by later commit transaction.
  *
- * NOTE: this function may sleep for memory allocation.
- *       if btrfs_qgroup_reserve_data() is called multiple times with
- *       same @reserved, caller must ensure when error happens it's OK
- *       to free *ALL* reserved space.
+ * - Commit transaction
+ *   This would free the meta_per_trans space.
+ *   In theory this shouldn't provide much space, but any more qgroup space
+ *   is needed.
  */
-int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
+static int try_flush_qgroup(struct btrfs_root *root)
+{
+	struct btrfs_trans_handle *trans;
+	int ret;
+
+	if (!is_fstree(root->root_key.objectid))
+		return 0;
+
+	/*
+	 * We don't want to run flush again and again, so if there is a running
+	 * one, we won't try to start a new flush, but exit directly.
+	 */
+	ret = mutex_trylock(&root->qgroup_flushing_mutex);
+	if (!ret) {
+		mutex_lock(&root->qgroup_flushing_mutex);
+		mutex_unlock(&root->qgroup_flushing_mutex);
+		return 0;
+	}
+
+	ret = btrfs_start_delalloc_snapshot(root);
+	if (ret < 0)
+		goto unlock;
+	btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
+
+	trans = btrfs_join_transaction(root);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto unlock;
+	}
+
+	ret = btrfs_commit_transaction(trans);
+unlock:
+	mutex_unlock(&root->qgroup_flushing_mutex);
+	return ret;
+}
+
+static int qgroup_reserve_data(struct btrfs_inode *inode,
 			struct extent_changeset **reserved_ret, u64 start,
 			u64 len)
 {
@@ -3573,6 +3615,37 @@ int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
 	return ret;
 }
 
+/*
+ * Reserve qgroup space for range [start, start + len).
+ *
+ * This function will either reserve space from related qgroups or doing
+ * nothing if the range is already reserved.
+ *
+ * Return 0 for successful reserve
+ * Return <0 for error (including -EQUOT)
+ *
+ * NOTE: This function may sleep for memory allocation, dirty page flushing and
+ *	 commit transaction. So caller should not hold any dirty page locked.
+ */
+int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
+			struct extent_changeset **reserved_ret, u64 start,
+			u64 len)
+{
+	int ret;
+
+	ret = qgroup_reserve_data(inode, reserved_ret, start, len);
+	if (!ret)
+		return ret;
+
+	if (ret < 0 && ret != -EDQUOT)
+		return ret;
+
+	ret = try_flush_qgroup(inode->root);
+	if (ret < 0)
+		return ret;
+	return qgroup_reserve_data(inode, reserved_ret, start, len);
+}
+
 /* Free ranges specified by @reserved, normally in error path */
 static int qgroup_free_reserved_data(struct btrfs_inode *inode,
 			struct extent_changeset *reserved, u64 start, u64 len)
@@ -3740,7 +3813,7 @@ static int sub_root_meta_rsv(struct btrfs_root *root, int num_bytes,
 	return num_bytes;
 }
 
-int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
+static int qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
 				enum btrfs_qgroup_rsv_type type, bool enforce)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -3767,6 +3840,23 @@ int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
 	return ret;
 }
 
+int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
+				enum btrfs_qgroup_rsv_type type, bool enforce)
+{
+	int ret;
+
+	ret = qgroup_reserve_meta(root, num_bytes, type, enforce);
+	if (!ret)
+		return ret;
+	if (ret < 0 && ret != -EDQUOT)
+		return ret;
+
+	ret = try_flush_qgroup(root);
+	if (ret < 0)
+		return ret;
+	return qgroup_reserve_meta(root, num_bytes, type, enforce);
+}
+
 void btrfs_qgroup_free_meta_all_pertrans(struct btrfs_root *root)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
