Re: [PATCH v3 1/4] btrfs: zoned: track only sequential zones as active

["Naohiro Aota" <Naohiro.Aota@wdc.com>]

On Fri Aug 28, 2026 at 12:51 PM JST, Dongjiang Zhu wrote:
> The runtime activation and finish paths apply active-zone accounting to
> both conventional and sequential stripes.
>
> At mount, however, active_zones_left is rebuilt from device zone
> conditions.  Conventional zones report NOT_WP and are therefore not
> included.  Meanwhile, all-conventional block groups are marked active
> and added to zone_active_bgs, so mount recovery still decreases
> reserved_active_zones for their metadata and system stripes.
>
> The two counters can therefore diverge across a remount.
>
> Each unmatched reservation decrement lets data consume one more
> sequential active-zone slot.  Once the reservation becomes negative,
> data can exhaust all such slots.
>
> A later transition from a conventional metadata or system target to a
> sequential one can then fail, because finishing the conventional target
> does not release a sequential active-zone slot.
>
> If this happens during synchronous transaction writeback,
> btrfs_check_meta_write_pointer() returns -EAGAIN.  The transaction is
> then aborted and the filesystem is forced read-only.
>
> The reservation mismatch was reproduced by creating small files with
> large xattrs in batches, syncing them and remounting an HC620 filesystem
> using SINGLE profiles:
>
>   active_zones_left:     126
>   reserved_active_zones: 3 -> -8
>
> The active list contained one partially used conventional system block
> group, nine full conventional metadata block groups and one partially
> used conventional metadata block group.
>
> To keep both counters based on the same physical resource, use
> sequential stripes as the unit of active-zone tracking.  Accordingly, do
> not mark all-conventional block groups active, and update the active-zone
> bitmap and non-data reservation only for sequential stripes during
> activation, finish and mount recovery.
>
> Assisted-by: LLM
> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Signed-off-by: Dongjiang Zhu <zhudongjiang@fygo.io>
> ---
>  fs/btrfs/zoned.c | 59 ++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 42 insertions(+), 17 deletions(-)

I'm sorry to miss this version, but the same comment applies on this
version too.

https://lore.kernel.org/linux-btrfs/DL0AVDP5O9C2.1VT2TYQXCL4B4@wdc.com/