Re: [PATCH v2 0/8] btrfs: zoned: unify relocation on a zoned and regular FS

[David Sterba <dsterba@suse.cz>]

On Thu, Sep 09, 2021 at 01:19:24AM +0900, Johannes Thumshirn wrote:
> A while ago David reported a bug in zoned btrfs' relocation code. The bug is
> triggered because relocation on a zoned filesystem does not preallocate the
> extents it copies and a writeback process running in parallel can cause a
> split of the written extent. But splitting extents is currently not allowed on
> relocation as it assumes a one to one copy of the relocated extents.
> 
> This causes transaction aborts and the filessytem switching to read-only in
> order to prevent further damage.
> 
> The first patch in this series is just a preparation to avoid overly long
> lines in follow up patches. Patch number two adds a dedicated block group for
> relocation on a zoned filesystem. Number three excludes multiple processes
> from adding pages to a relocation inode in a zoned filesystem. Patch four
> switches relocation from REQ_OP_ZONE_APPEND to regular REQ_OP_WRITE, five
> prepares an ASSERT()ion that we can enter the nocow path on a zoned filesystem
> under very special circumstances and the sixth patch then switches the
> relocation code for a zoned filesystem to using the same code path as we use
> on a non zoned filesystem. As the changes before have made the prerequisites
> to do so. The last two patches in this series are just a simple rename of a
> function whose name we have twice in the btrfs codebase but with a different
> purpose in different files and a cleanup of a complicated boolean comparison
> into an if to make it stand out.
> 
> Changes to v1:
> - Added patches 3 and 8
> - Added comments to patches 4 and 5 (Naohiro)
> - Move btrfs_clear_data_reloc_bg() out of line (David)
> - Untangle the 'skip' assing into an if (David)
> - Commented new fs_info members (David)
> 
> Johannes Thumshirn (8):
>   btrfs: introduce btrfs_is_data_reloc_root
>   btrfs: zoned: add a dedicated data relocation block group
>   btrfs: zoned: only allow one process to add pages to a relocation
>     inode
>   btrfs: zoned: use regular writes for relocation
>   btrfs: check for relocation inodes on zoned btrfs in should_nocow
>   btrfs: zoned: allow preallocation for relocation inodes
>   btrfs: rename setup_extent_mapping in relocation code
>   btrfs: zoned: let the for_treelog test in the allocator stand out

I did a few minor fixups, patches moved from topic branch to misc-next.
Thanks.