Re: [PATCH v4 6/7] btrfs: qgroup: Use delayed subtree rescan for balance

[David Sterba <dsterba@suse.cz>]

On Tue, Jan 15, 2019 at 04:16:03PM +0800, Qu Wenruo wrote:
> +int btrfs_qgroup_trace_subtree_after_cow(struct btrfs_trans_handle *trans,
> +					 struct btrfs_root *root,
> +					 struct extent_buffer *subv_eb)
> +{
> +	struct btrfs_fs_info *fs_info = root->fs_info;
> +	struct btrfs_qgroup_swapped_blocks *blocks = &root->swapped_blocks;
> +	struct btrfs_qgroup_swapped_block *block;
> +	struct extent_buffer *reloc_eb = NULL;
> +	struct rb_node *n;

Please don't use single letter variable here

> +	bool found = false;
> +	bool swapped = false;
> +	int level = btrfs_header_level(subv_eb);
> +	int ret = 0;
> +	int i;
> +
> +	if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
> +		return 0;
> +	if (!is_fstree(root->root_key.objectid) || !root->reloc_root)
> +		return 0;
> +
> +	spin_lock(&blocks->lock);
> +	if (!blocks->swapped) {
> +		spin_unlock(&blocks->lock);
> +		goto out;

I think you can return here directly, as this is a shortcut and there's
no state that would need to be cleaned up (ret is still 0).

> +	}
> +	n = blocks->blocks[level].rb_node;
> +
> +	while (n) {
> +		block = rb_entry(n, struct btrfs_qgroup_swapped_block, node);
> +		if (block->subv_bytenr < subv_eb->start)
> +			n = n->rb_left;
> +		else if (block->subv_bytenr > subv_eb->start)
> +			n = n->rb_right;
> +		else {
> +			found = true;
> +			break;
> +		}
> +	}
> +	if (!found) {
> +		spin_unlock(&blocks->lock);
> +		goto out;
> +	}
> +	/* Found one, remove it from @blocks first and update blocks->swapped */
> +	rb_erase(&block->node, &blocks->blocks[level]);
> +	for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
> +		if (RB_EMPTY_ROOT(&blocks->blocks[i])) {
> +			swapped = true;
> +			break;
> +		}
> +	}
> +	blocks->swapped = swapped;
> +	spin_unlock(&blocks->lock);
> +
> +	/* Read out reloc subtree root */
> +	reloc_eb = read_tree_block(fs_info, block->reloc_bytenr,
> +				   block->reloc_generation, block->level,
> +				   &block->first_key);
> +	if (IS_ERR(reloc_eb)) {
> +		ret = PTR_ERR(subv_eb);
> +		reloc_eb = NULL;
> +		goto free_out;
> +	}
> +	if (!extent_buffer_uptodate(reloc_eb)) {
> +		ret = -EIO;
> +		goto free_out;
> +	}
> +
> +	ret = qgroup_trace_subtree_swap(trans, reloc_eb, subv_eb,
> +			block->last_snapshot, block->trace_leaf);
> +free_out:
> +	kfree(block);
> +	free_extent_buffer(reloc_eb);
> +out:
> +	if (ret < 0) {
> +		btrfs_err_rl(fs_info,
> +			     "failed to account subtree at bytenr %llu: %d",
> +			     subv_eb->start, ret);
> +		fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
> +	}
> +	return ret;
> +}