Re: [PATCH PoC 1/9] btrfs: introduce BTRFS_IOC_SCRUB_FS family of ioctls

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> The new ioctls are to address the disadvantages of the existing
> btrfs_scrub_dev():
> 
> a One thread per-device
>   This can cause multiple block groups to be marked read-only for scrub,
>   reducing available space temporarily.
> 
>   This also causes higher CPU/IO usage.
>   For scrub, we should use the minimal amount of CPU and cause less
>   IO when possible.
> 
> b Extra IO for RAID56
>   For data stripes, we will cause at least 2x IO if we run "btrfs scrub
>   start <mnt>".
>   1x from scrubbing the device of data stripe.
>   The other 1x from scrubbing the parity stripe.
> 
>   This duplicated IO should definitely be avoided
> 
> c Bad progress report for RAID56
>   We can not report any repaired P/Q bytes at all.
> 
> The a and b will be addressed by the new one thread per-fs
> btrfs_scrub_fs ioctl.
> 
> While c will be addressed by the new btrfs_scrub_fs_progress structure,
> which has better comments and classification for all errors.
> 
> This patch is only a skeleton for the new family of ioctls, will return
> -EOPNOTSUPP for now.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/ioctl.c           |   6 ++
>  include/uapi/linux/btrfs.h | 173 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 179 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index fe0cc816b4eb..3df3bcdf06eb 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -5508,6 +5508,12 @@ long btrfs_ioctl(struct file *file, unsigned int
>  		return btrfs_ioctl_scrub_cancel(fs_info);
>  	case BTRFS_IOC_SCRUB_PROGRESS:
>  		return btrfs_ioctl_scrub_progress(fs_info, argp);
> +	case BTRFS_IOC_SCRUB_FS:
> +		return -EOPNOTSUPP;
> +	case BTRFS_IOC_SCRUB_FS_CANCEL:
> +		return -EOPNOTSUPP;
> +	case BTRFS_IOC_SCRUB_FS_PROGRESS:
> +		return -EOPNOTSUPP;

Could we add suspend/resume for scrub when huge filesysem?

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2022/09/09