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

[Johannes Thumshirn <johannes.thumshirn@wdc.com>]

On Mon, Aug 24, 2026 at 02:49:53PM +0800, Dongjiang Zhu wrote:
> [CAUSE]
> 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.
> 
> [BUG]
> 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.
> 
> [FIX]
> Use sequential stripes as the unit of active-zone tracking.
> 
> Do not mark all-conventional block groups active.  Only sequential
> stripes update the active-zone bitmap and non-data reservation during
> activation, finish and mount recovery.
> 
> Assisted-by: LLM
> Signed-off-by: Dongjiang Zhu <zhudongjiang@fygo.io>

Looks good, two small nits though in case you need to resend the series:
1) Please don't do the [CAUSE], [BUG], [FIX] thingy, I know Qu does it but
noone else does that.
2) We now have a repeated pattern of:

  if (!btrfs_dev_is_sequential())
	return
  if (max_active_zones)
        return

Maybe have a helper for that? Something like

static inline bool btrfs_needs_active_zone_tracking(struct btrfs_device *dev,
						    u64 physical)
{
	if (!btrfs_dev_is_sequential(dev, physical))
		return false;

	if (dev->zone_info->max_active_zones == 0)
		return false;

	return true;
}

Otherwise looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>