Re: [PATCH RFC PATCH 3/3] btrfs: zoned: kick cleaner kthread if low on space

[David Sterba <dsterba@suse.cz>]

On Thu, Mar 28, 2024 at 02:56:33PM +0100, Johannes Thumshirn wrote:
> From: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> 
> Kick the cleaner kthread on chunk allocation if we're slowly running out
> of usable space on a zoned filesystem.

For zoned mode it makes more sense, as Boris noted it could be done for
non-zoned too but maybe based on additional criteria as reusing the
space is easier.

Also cleaner does several things so it may start doing subvolume
cleaning or defragmentation at the worst time.

> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/btrfs/zoned.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index fb8707f4cab5..25c1a17873db 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -1040,6 +1040,7 @@ int btrfs_reset_sb_log_zones(struct block_device *bdev, int mirror)
>  u64 btrfs_find_allocatable_zones(struct btrfs_device *device, u64 hole_start,
>  				 u64 hole_end, u64 num_bytes)
>  {
> +	struct btrfs_fs_info *fs_info = device->fs_info;
>  	struct btrfs_zoned_device_info *zinfo = device->zone_info;
>  	const u8 shift = zinfo->zone_size_shift;
>  	u64 nzones = num_bytes >> shift;
> @@ -1051,6 +1052,11 @@ u64 btrfs_find_allocatable_zones(struct btrfs_device *device, u64 hole_start,
>  	ASSERT(IS_ALIGNED(hole_start, zinfo->zone_size));
>  	ASSERT(IS_ALIGNED(num_bytes, zinfo->zone_size));
>  
> +	if (!test_bit(BTRFS_FS_CLEANER_RUNNING, &fs_info->flags) &&
> +	    btrfs_zoned_should_reclaim(fs_info)) {
> +		wake_up_process(fs_info->cleaner_kthread);

You can drop the BTRFS_FS_CLEANER_RUNNING condition, this is not a
performance sensitive where the wake up of an already running process
would hurt.

> +	}
> +
>  	while (pos < hole_end) {
>  		begin = pos >> shift;
>  		end = begin + nzones;
> 
> -- 
> 2.35.3
>