Re: [PATCH v4 5/6] btrfs: stop running all delayed refs during snapshot

[Nikolay Borisov <nborisov@suse.com>]

On 17.12.20 г. 16:36 ч., Josef Bacik wrote:
> This was added a very long time ago to work around issues with delayed
> refs and with qgroups.  Both of these issues have since been properly
> fixed, so all this does is cause a lot of lock contention with anybody
> else who is running delayed refs.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Codewise it's ok, however I would have liked a better reference to the 2
problems being fixed, I'd assume same applies to David. SO it seems the
first delayed refs run was added due to :

361048f586f5 ("Btrfs: fix full backref problem when inserting shared
block reference") and the 2nd one by d67263354541 ("btrfs: qgroup: Make
snapshot accounting work with new extent-oriented qgroup.")


However there is no indication what code superseded the need for those 2
commits.


> ---
>  fs/btrfs/transaction.c | 12 ------------
>  1 file changed, 12 deletions(-)
> 
> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
> index 4776e055f7f9..6e3abe9b74c0 100644
> --- a/fs/btrfs/transaction.c
> +++ b/fs/btrfs/transaction.c
> @@ -1686,12 +1686,6 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
>  		goto fail;
>  	}
>  
> -	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
> -	if (ret) {
> -		btrfs_abort_transaction(trans, ret);
> -		goto fail;
> -	}
> -
>  	/*
>  	 * Do special qgroup accounting for snapshot, as we do some qgroup
>  	 * snapshot hack to do fast snapshot.
> @@ -1739,12 +1733,6 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
>  		}
>  	}
>  
> -	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
> -	if (ret) {
> -		btrfs_abort_transaction(trans, ret);
> -		goto fail;
> -	}
> -
>  fail:
>  	pending->error = ret;
>  dir_item_existed:
>