Re: [PATCH v3 3/5] btrfs: zoned: always set data_relocation_bg

["Naohiro Aota" <Naohiro.Aota@wdc.com>]

On Fri May 22, 2026 at 6:02 PM JST, 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.
>
> There is actually no point in looking for the second empty DATA block
> group as new DATA allocations will just allocate a new chunk for it. Pick
> the first DATA block-group without any allocations done and set it as
> relocation block-group.

I think we can add context here.

At first, the commit 694ce5e143d6 ("btrfs: zoned: reserve data_reloc
block group on mount") introduced the functionality. At that time, we
took second unused (used == 0) block group, as the first one might be
a block group used for normal data.

Later, commit daa0fde32235 ("btrfs: zoned: fix data relocation block
group reservation") switched to look for an empty block group
(alloc_offset == 0). At this point, there is no reason taking the second
one anymore. So, this commit is fixing an issue in commit daa0fde32235.

>
> Singed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/btrfs/zoned.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 16dd87aa06f2..a4d2fb774f72 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -2763,7 +2763,6 @@ void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info)
>  	struct btrfs_block_group *bg;
>  	struct list_head *bg_list;
>  	u64 alloc_flags;
> -	bool first = true;
>  	bool did_chunk_alloc = false;
>  	int index;
>  	int ret;
> @@ -2784,13 +2783,9 @@ void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info)

Could you please fix the comment here?

	/* Scan the data space_info to find empty block groups. Take the second one. */

Other than that,

Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>

>  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;
> +		if (bg->alloc_offset != 0)
>  			continue;
> -		}
>  
>  		if (space_info == data_sinfo) {
>  			/* Migrate the block group to the data relocation space_info. */
> @@ -2849,7 +2844,6 @@ void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info)
>  		 * We allocated a new block group in the data relocation space_info. We
>  		 * can take that one.
>  		 */
> -		first = false;
>  		did_chunk_alloc = true;
>  		goto again;
>  	}