Re: [PATCH v5 13/18] btrfs: record simple quota deltas

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Jul 27, 2023 at 03:13:00PM -0700, Boris Burkov wrote:
> At the moment that we run delayed refs, we make the final ref-count
> based decision on creating/removing extent (and metadata) items.
> Therefore, it is exactly the spot to hook up simple quotas.
> 
> There are a few important subtleties to the fields we must collect to
> accurately track simple quotas, particularly when removing an extent.
> When removing a data extent, the ref could be in any tree (due to
> reflink, for example) and so we need to recover the owning root id from
> the owner ref item. When removing a metadata extent, we know the owning
> root from the owner field in the header when we create the delayed ref,
> so we can recover it from there.
> 
> We must also be careful to handle reservations properly to not leaked
> reserved space. The happy path is freeing the reservation when the
> simple quota delta runs on a data extent. If that doesn't happen, due to
> refs canceling out or some error, the ref head already has the
> must_insert_reserved machinery to handle this, so we piggy back on that
> and use it to clean up the reserved data.
> 
> Signed-off-by: Boris Burkov <boris@bur.io>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef