Re: [PATCH 2/5] btrfs: allow block group background reclaim for !zoned fs'es

[Josef Bacik <josef@toxicpanda.com>]

On Mon, Mar 21, 2022 at 09:14:11AM -0700, Johannes Thumshirn wrote:
> From: Josef Bacik <josef@toxicpanda.com>
> 
> We have found this feature invaluable at Facebook due to how our
> workload interacts with the allocator.  We have been using this in
> production for months with only a single problem that has already been
> fixed.  This will allow us to set a threshold for block groups to be
> automatically relocated even if we don't have zoned devices.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/block-group.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index 59f18a10fd5f..628741ecb97b 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -3208,6 +3208,31 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans)
>  	return ret;
>  }
>  
> +static inline bool should_reclaim_block_group(struct btrfs_block_group *block_group,
> +					      u64 bytes_freed)
> +{
> +	const struct btrfs_space_info *space_info = block_group->space_info;
> +	const int reclaim_thresh = READ_ONCE(space_info->bg_reclaim_threshold);
> +	const u64 new_val = block_group->used;
> +	const u64 old_val = new_val + bytes_freed;
> +	u64 thresh;
> +

Actually do we want to do a

if (btrfs_zoned())
	return false;

here and leave the auto reclaim zoned behavior the way it is?  Or do you want to
delete your stuff and rely on this as the way that we setup zoned block groups
for relocation?  If we use this then you could make the
fs_info->bg_reclaim_threshold also apply here.  Thanks,

Josef