Re: [PATCH 01/22] btrfs: add btrfs_delete_ref_head helper

[Nikolay Borisov <nborisov@suse.com>]

On 19.07.2018 17:49, Josef Bacik wrote:
> From: Josef Bacik <jbacik@fb.com>
> 
> We do this dance in cleanup_ref_head and check_ref_cleanup, unify it
> into a helper and cleanup the calling functions.
> 
> Signed-off-by: Josef Bacik <jbacik@fb.com>
> ---
>  fs/btrfs/delayed-ref.c | 14 ++++++++++++++
>  fs/btrfs/delayed-ref.h |  3 ++-
>  fs/btrfs/extent-tree.c | 24 ++++--------------------
>  3 files changed, 20 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index 03dec673d12a..e1b322d651dd 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -393,6 +393,20 @@ btrfs_select_ref_head(struct btrfs_trans_handle *trans)
>  	return head;
>  }
>  
> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
> +			   struct btrfs_delayed_ref_head *head)
> +{
> +	lockdep_assert_held(&delayed_refs->lock);
> +	lockdep_assert_held(&head->lock);
> +
> +	rb_erase(&head->href_node, &delayed_refs->href_root);
> +	RB_CLEAR_NODE(&head->href_node);
> +	atomic_dec(&delayed_refs->num_entries);
> +	delayed_refs->num_heads--;
> +	if (head->processing == 0)
> +		delayed_refs->num_heads_ready--;
> +}
> +
>  /*
>   * Helper to insert the ref_node to the tail or merge with tail.
>   *
> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
> index ea1aecb6a50d..36318182e4ec 100644
> --- a/fs/btrfs/delayed-ref.h
> +++ b/fs/btrfs/delayed-ref.h
> @@ -263,7 +263,8 @@ static inline void btrfs_delayed_ref_unlock(struct btrfs_delayed_ref_head *head)
>  {
>  	mutex_unlock(&head->mutex);
>  }
> -
> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
> +			   struct btrfs_delayed_ref_head *head);
>  
>  struct btrfs_delayed_ref_head *
>  btrfs_select_ref_head(struct btrfs_trans_handle *trans);
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 3d9fe58c0080..ccaccd78534e 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2577,12 +2577,9 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans,
>  		spin_unlock(&delayed_refs->lock);
>  		return 1;
>  	}
> -	delayed_refs->num_heads--;
> -	rb_erase(&head->href_node, &delayed_refs->href_root);
> -	RB_CLEAR_NODE(&head->href_node);
> -	spin_unlock(&head->lock);
> +	btrfs_delete_ref_head(delayed_refs, head);
>  	spin_unlock(&delayed_refs->lock);
> -	atomic_dec(&delayed_refs->num_entries);
> +	spin_unlock(&head->lock);
>  
>  	trace_run_delayed_ref_head(fs_info, head, 0);
>  
> @@ -7122,22 +7119,9 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
>  	if (!mutex_trylock(&head->mutex))
>  		goto out;
>  
> -	/*
> -	 * at this point we have a head with no other entries.  Go
> -	 * ahead and process it.
> -	 */
> -	rb_erase(&head->href_node, &delayed_refs->href_root);
> -	RB_CLEAR_NODE(&head->href_node);
> -	atomic_dec(&delayed_refs->num_entries);
> -
> -	/*
> -	 * we don't take a ref on the node because we're removing it from the
> -	 * tree, so we just steal the ref the tree was holding.
> -	 */
> -	delayed_refs->num_heads--;
> -	if (head->processing == 0)
> -		delayed_refs->num_heads_ready--;

In cleanup_ref_head we don't have the num_heads_ready-- code so this is
not pure consolidation but changes the behavior to a certain extent. It
seems this patch is also fixing a bug w.r.t num_heads_ready counts if
so, this needs to be documented in the changelog.

> +	btrfs_delete_ref_head(delayed_refs, head);
>  	head->processing = 0;
> +
>  	spin_unlock(&head->lock);
>  	spin_unlock(&delayed_refs->lock);
>  
>