Re: [PATCH 2/2] btrfs: zoned: limit ordered extent to zoned append size

[David Sterba <dsterba@suse.cz>]

On Tue, Jun 01, 2021 at 10:02:10PM +0900, Johannes Thumshirn wrote:
> Damien reported a test failure with btrfs/209. The test itself ran fine,
> but the fsck run afterwards reported a corrupted filesystem.
> 
> The filesystem corruption happens because we're splitting an extent and
> then writing the extent twice. We have to split the extent though, because
> we're creating too large extents for a REQ_OP_ZONE_APPEND operation.
> 
> When dumping the extent tree, we can see two EXTENT_ITEMs at the same
> start address but different lengths.
> 
> $ btrfs inspect dump-tree /dev/nullb1 -t extent
> ...
>    item 19 key (269484032 EXTENT_ITEM 126976) itemoff 15470 itemsize 53
>            refs 1 gen 7 flags DATA
>            extent data backref root FS_TREE objectid 257 offset 786432 count 1
>    item 20 key (269484032 EXTENT_ITEM 262144) itemoff 15417 itemsize 53
>            refs 1 gen 7 flags DATA
>            extent data backref root FS_TREE objectid 257 offset 786432 count 1
> 
> On a zoned filesystem, limit the size of an ordered extent to the maximum
> size that can be issued as a single REQ_OP_ZONE_APPEND operation.
> 
> Note: This patch breaks fstests btrfs/079, as it increases the number of
> on-disk extents from 80 to 83 per 10M write.
> 
> Reported-by: Damien Le Moal <damien.lemoal@wdc.com>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/btrfs/ctree.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 5d0398528a7a..6fbafaaebda0 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1373,7 +1373,10 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_fs_info *info)
>  
>  static inline u64 btrfs_get_max_extent_size(struct btrfs_fs_info *fs_info)
>  {
> -	return BTRFS_MAX_EXTENT_SIZE;
> +	if (!fs_info || !fs_info->max_zone_append_size)
> +		return BTRFS_MAX_EXTENT_SIZE;
> +	return min_t(u64, BTRFS_MAX_EXTENT_SIZE,
> +		     ALIGN_DOWN(fs_info->max_zone_append_size, PAGE_SIZE));

Should this be set only once in btrfs_check_zoned_mode ?

>  }
>  
>  /*
> -- 
> 2.31.1
>