Re: [PATCH] btrfs: zoned: don't zone append to conventional zone

[hch <hch@lst.de>]

On Tue, Dec 02, 2025 at 01:43:07PM +0000, Johannes Thumshirn wrote:
> On 12/2/25 2:29 PM, Christoph Hellwig wrote:
> > On Tue, Dec 02, 2025 at 11:16:31AM +0100, Johannes Thumshirn wrote:
> >> In case of a zoned RAID, it can happen that a data write is targeting a
> >> sequential write required zone and a conventional zone. In this case the
> >> bio will be marked as REQ_OP_ZONE_APPEND but for the conventional zone,
> >> this needs to be REQ_OP_WRITE.
> >>
> >> This is a partial revert of commit d5e4377d5051 ("btrfs: split zone append
> >> bios in btrfs_submit_bio") which was introduced before zoned RAID.
> > Hmm, how does the BLOCK_GROUP_FLAG_SEQUENTIAL_ZONE flag used by
> > btrfs_use_zone_append actually work for the raid code?
> 
> 
> If one of the zones backing the block-group is sequential the flag is 
> set, see btrfs_load_block_group_zone_info().
> 
> > Either way, this is a bit ugly as we now special case zone append in
> > multiple places.  Can we just pass the use_append flag down to
> > btrfs_submit_dev_bio and only set REQ_OP_ZONE_APPEND there to keep it
> > all tidy?
> Let me have a look how we can make that non-ugly. Or just use 
> btrfs_dev_is_sequential() in btrfs_submit_dev_bio(), which is probably 
> nicer as it doesn't need a rbtree lookup for the block-group.

Well, it still needs to check all the other conditions that prohibit
using zone append (metadata, reloc inode, ...)