Re: [PATCH 5/5] btrfs: run btrfs_try_granting_tickets if a priority ticket fails

Nikolay Borisov
2020-03-17T12:59:24Z

On 13.03.20 г. 21:58 ч., Josef Bacik wrote:
> With normal tickets we could have a large reservation at the front of
> the list that is unable to be satisfied, but a smaller ticket later on
> that can be satisfied. The way we handle this is to run
> btrfs_try_granting_tickets() in maybe_fail_all_tickets().
>
> However no such protection exists for priority tickets. Fix this by
> handling it in handle_reserve_ticket(). If we've returned after
> attempting to flush space in a priority related way, we'll still be on
> the priority list and need to be removed.
>
> We rely on the flushing to free up space and wake the ticket, but if
> there is not enough space to reclaim _but_ there's enough space in the
> space_info to handle subsequent reservations then we would have gotten
> an ENOSPC erroneously.
>
> Address this by catching where we are still on the list, meaning we were
> a priority ticket, and removing ourselves and then running
> btrfs_try_granting_tickets(). This will handle this particular corner
> case.
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>