Re: [PATCH 3/7] btrfs: zoned: always set data_relocation_bg

[Boris Burkov <boris@bur.io>]

On Wed, May 13, 2026 at 02:34:41PM +0200, Johannes Thumshirn wrote:
> When searching for a data relocation block-group on mount,
> btrfs_zoned_reserve_data_reloc_bg() is looking for the first empty DATA
> block-group. But it first checks if the block-group is empty and if yes
> continues the search, and then checks if it is the first DATA block-group.
> 
> Reverse the order, first check if it is the first DATA block-group found
> and skip, then check if the block-group is empty. This enusres that there
> is always a DATA block-group set as data_relocation_bg in the filesystem.

You want the second empty block group? or the first? if you want the
first, then checking for "first" ever seems pointless. If you want the
second, then I think you need to layer the "if (first)" inside the
successful non-empty check?

As is, it just unilaterally skips the first bg even if it's not empty
and will grab the first empty one. It makes sense to not use the first
empty for reloc (that's for alloc presumably) but I don't see why just
plain skipping the first one makes sense.

> 
> Singed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/btrfs/zoned.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 16dd87aa06f2..0b80b498fb85 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -2784,14 +2784,14 @@ void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info)
>  again:
>  	bg_list = &space_info->block_groups[index];
>  	list_for_each_entry(bg, bg_list, list) {
> -		if (bg->alloc_offset != 0)
> -			continue;
> -
>  		if (first) {
>  			first = false;
>  			continue;
>  		}
>  
> +		if (bg->alloc_offset != 0)
> +			continue;
> +
>  		if (space_info == data_sinfo) {
>  			/* Migrate the block group to the data relocation space_info. */
>  			struct btrfs_space_info *reloc_sinfo = data_sinfo->sub_group[0];
> -- 
> 2.54.0
>