Re: [PATCH v4 6/7] btrfs: Introduce new incompat feature, SKINNY_BG_TREE, to hugely reduce mount time

From: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
To: Qu Wenruo <wqu@suse.com>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH v4 6/7] btrfs: Introduce new incompat feature, SKINNY_BG_TREE, to hugely reduce mount time
Date: Tue, 5 May 2020 19:10:53 +0000	[thread overview]
Message-ID: <SN4PR0401MB359872C31B77B386876AC78F9BA70@SN4PR0401MB3598.namprd04.prod.outlook.com> (raw)
In-Reply-To: 20200504235825.4199-7-wqu@suse.com

On 05/05/2020 01:58, Qu Wenruo wrote:
> int btrfs_read_block_groups(struct btrfs_fs_info *info)
>   {
>   	struct btrfs_path *path;
> @@ -2022,20 +2124,27 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
>   	if (btrfs_test_opt(info, CLEAR_CACHE))
>   		need_clear = 1;
>   
> -	while (1) {
> -		ret = find_first_block_group(info, path, &key);
> -		if (ret > 0)
> -			break;
> -		if (ret != 0)
> -			goto error;
> +	if (btrfs_fs_incompat(info, SKINNY_BG_TREE)) {
> +		path->reada = READA_FORWARD;
> +		ret = read_skinny_block_groups(info, path, need_clear);
> +	} else {
> +		while (1) {
> +			ret = find_first_block_group(info, path, &key);
> +			if (ret > 0)
> +				break;
> +			if (ret != 0)
> +				goto error;
>   
> -		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
> -		ret = read_one_block_group(info, path, &key, need_clear);
> -		if (ret < 0)
> -			goto error;
> -		key.objectid += key.offset;
> -		key.offset = 0;
> -		btrfs_release_path(path);
> +			btrfs_item_key_to_cpu(path->nodes[0], &key,
> +						path->slots[0]);
> +			ret = read_one_block_group(info, path, &key,
> +						need_clear);
> +			if (ret < 0)
> +				goto error;
> +			key.objectid += key.offset;
> +			key.offset = 0;
> +			btrfs_release_path(path);
> +		}
>   	}
>   

It might be worth considering to move the 'else' path into a function on 
it's own, similar what you did with read_skinny_block_groups().