Re: [PATCH 14/18] btrfs: record simple quota deltas

[Josef Bacik <josef@toxicpanda.com>]

On Wed, Jul 05, 2023 at 04:20:51PM -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>
> ---
>  fs/btrfs/delayed-ref.c |  3 ++
>  fs/btrfs/delayed-ref.h |  6 ++++
>  fs/btrfs/extent-tree.c | 79 +++++++++++++++++++++++++++++++++++++-----
>  3 files changed, 80 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index 89641bcd6841..04e124a93049 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -735,6 +735,9 @@ static void init_delayed_ref_head(struct btrfs_delayed_ref_head *head_ref,
>  	head_ref->bytenr = bytenr;
>  	head_ref->num_bytes = num_bytes;
>  	head_ref->ref_mod = count_mod;
> +	head_ref->reserved_bytes = 0;
> +	if (reserved)
> +		head_ref->reserved_bytes = reserved;

This is just

head_ref->reserved_bytes = reserved;

Thanks,

Josef