Re: [PATCH 27/40] btrfs: clean up the raid map handling __btrfs_map_block

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/3/22 23:55, Christoph Hellwig wrote:
> Clear need_raid_map early instead of repeating the same conditional over
> and over.

I had a more comprehensive cleanup, but only for scrub:
https://lore.kernel.org/linux-btrfs/cover.1646984153.git.wqu@suse.com/

All profiles are split into 3 categories:

- Simple mirror
   Single, DUP, RAID1*.

- Simple stripe
   RAID0 and RAID10
   Inside each data stripe, it's just simple mirror then.

- RAID56
   And for mirror_num == 0/1 cases, inside one data stripe it's still
   simple mirror.

Maybe we can follow the same ideas here?

Thanks,
Qu


>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/btrfs/volumes.c | 60 ++++++++++++++++++++++------------------------
>   1 file changed, 29 insertions(+), 31 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 1cf0914b33847..cc9e2565e4b64 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6435,6 +6435,10 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
>
>   	map = em->map_lookup;
>
> +	if (!(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) ||
> +	    (!need_full_stripe(op) && mirror_num <= 1))
> +		need_raid_map = 0;
> +
>   	*length = geom.len;
>   	stripe_len = geom.stripe_len;
>   	stripe_nr = geom.stripe_nr;
> @@ -6509,37 +6513,32 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
>   					      dev_replace_is_ongoing);
>   			mirror_num = stripe_index - old_stripe_index + 1;
>   		}
> +	} else if (need_raid_map) {
> +		/* push stripe_nr back to the start of the full stripe */
> +		stripe_nr = div64_u64(raid56_full_stripe_start,
> +				      stripe_len * data_stripes);
>
> -	} else if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
> -		if (need_raid_map && (need_full_stripe(op) || mirror_num > 1)) {
> -			/* push stripe_nr back to the start of the full stripe */
> -			stripe_nr = div64_u64(raid56_full_stripe_start,
> -					stripe_len * data_stripes);
> -
> -			/* RAID[56] write or recovery. Return all stripes */
> -			num_stripes = map->num_stripes;
> -			max_errors = nr_parity_stripes(map);
> -
> -			*length = map->stripe_len;
> -			stripe_index = 0;
> -			stripe_offset = 0;
> -		} else {
> -			/*
> -			 * Mirror #0 or #1 means the original data block.
> -			 * Mirror #2 is RAID5 parity block.
> -			 * Mirror #3 is RAID6 Q block.
> -			 */
> -			stripe_nr = div_u64_rem(stripe_nr,
> -					data_stripes, &stripe_index);
> -			if (mirror_num > 1)
> -				stripe_index = data_stripes + mirror_num - 2;
> +		/* RAID[56] write or recovery. Return all stripes */
> +		num_stripes = map->num_stripes;
> +		max_errors = nr_parity_stripes(map);
>
> -			/* We distribute the parity blocks across stripes */
> -			div_u64_rem(stripe_nr + stripe_index, map->num_stripes,
> -					&stripe_index);
> -			if (!need_full_stripe(op) && mirror_num <= 1)
> -				mirror_num = 1;
> -		}
> +		*length = map->stripe_len;
> +		stripe_index = 0;
> +		stripe_offset = 0;
> +	} else if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
> +		/*
> +		 * Mirror #0 or #1 means the original data block.
> +		 * Mirror #2 is RAID5 parity block.
> +		 * Mirror #3 is RAID6 Q block.
> +		 */
> +		stripe_nr = div_u64_rem(stripe_nr, data_stripes, &stripe_index);
> +		if (mirror_num > 1)
> +			stripe_index = data_stripes + mirror_num - 2;
> +		/* We distribute the parity blocks across stripes */
> +		div_u64_rem(stripe_nr + stripe_index, map->num_stripes,
> +			    &stripe_index);
> +		if (!need_full_stripe(op) && mirror_num <= 1)
> +			mirror_num = 1;
>   	} else {
>   		/*
>   		 * after this, stripe_nr is the number of stripes on this
> @@ -6581,8 +6580,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
>   	}
>
>   	/* Build raid_map */
> -	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK && need_raid_map &&
> -	    (need_full_stripe(op) || mirror_num > 1)) {
> +	if (need_raid_map) {
>   		u64 tmp;
>   		unsigned rot;
>