Re: [PATCH] btrfs: annotate unlikely branches after V0 extent type removal

[Nikolay Borisov <nborisov@suse.com>]

On 26.06.2018 17:24, David Sterba wrote:
> The v0 extent type checks are the right case for the unlikely
> annotations as we don't expect to ever see them, so let's give the
> compiler some hint.
> 
> Signed-off-by: David Sterba <dsterba@suse.com>

The question is how helpful those unlikelies are in the generated code.
Also according to the comment about __cold annotation this already gives
the compiler a hint that any code leading to such a cold function is
already unlikely.

Anyways:

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

> ---
>  fs/btrfs/extent-tree.c | 8 ++++----
>  fs/btrfs/print-tree.c  | 2 +-
>  fs/btrfs/relocation.c  | 8 ++++----
>  3 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 8713a1693dfc..d3f7afe3a548 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -1310,7 +1310,7 @@ static noinline int remove_extent_data_ref(struct btrfs_trans_handle *trans,
>  		ref2 = btrfs_item_ptr(leaf, path->slots[0],
>  				      struct btrfs_shared_data_ref);
>  		num_refs = btrfs_shared_data_ref_count(leaf, ref2);
> -	} else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
> +	} else if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
>  		btrfs_print_v0_err(fs_info);
>  		btrfs_abort_transaction(trans, -EINVAL);
>  		return -EINVAL;
> @@ -1563,7 +1563,7 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
>  
>  	leaf = path->nodes[0];
>  	item_size = btrfs_item_size_nr(leaf, path->slots[0]);
> -	if (item_size < sizeof(*ei)) {
> +	if (unlikely(item_size < sizeof(*ei))) {
>  		err = -EINVAL;
>  		btrfs_print_v0_err(fs_info);
>  		btrfs_abort_transaction(trans, err);
> @@ -2269,7 +2269,7 @@ static int run_delayed_extent_op(struct btrfs_trans_handle *trans,
>  	leaf = path->nodes[0];
>  	item_size = btrfs_item_size_nr(leaf, path->slots[0]);
>  
> -	if (item_size < sizeof(*ei)) {
> +	if (unlikely(item_size < sizeof(*ei))) {
>  		err = -EINVAL;
>  		btrfs_print_v0_err(fs_info);
>  		btrfs_abort_transaction(trans, err);
> @@ -6811,7 +6811,7 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
>  
>  	leaf = path->nodes[0];
>  	item_size = btrfs_item_size_nr(leaf, extent_slot);
> -	if (item_size < sizeof(*ei)) {
> +	if (unlikely(item_size < sizeof(*ei))) {
>  		ret = -EINVAL;
>  		btrfs_print_v0_err(info);
>  		btrfs_abort_transaction(trans, ret);
> diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
> index 772560eecfa6..0dd44d161935 100644
> --- a/fs/btrfs/print-tree.c
> +++ b/fs/btrfs/print-tree.c
> @@ -52,7 +52,7 @@ static void print_extent_item(struct extent_buffer *eb, int slot, int type)
>  	u64 offset;
>  	int ref_index = 0;
>  
> -	if (item_size < sizeof(*ei)) {
> +	if (unlikely(item_size < sizeof(*ei))) {
>  		btrfs_print_v0_err(eb->fs_info);
>  		btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
>  	}
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index a8dddefaae99..381bd3c24249 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -832,7 +832,7 @@ struct backref_node *build_backref_tree(struct reloc_control *rc,
>  			goto next;
>  		} else if (key.type != BTRFS_TREE_BLOCK_REF_KEY) {
>  			goto next;
> -		} else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
> +		} else if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
>  			err = -EINVAL;
>  			btrfs_print_v0_err(rc->extent_root->fs_info);
>  			btrfs_handle_fs_error(rc->extent_root->fs_info, err,
> @@ -3325,7 +3325,7 @@ static int add_tree_block(struct reloc_control *rc,
>  			level = (int)extent_key->offset;
>  		}
>  		generation = btrfs_extent_generation(eb, ei);
> -	} else if (item_size == sizeof(struct btrfs_extent_item_v0)) {
> +	} else if (unlikely(item_size == sizeof(struct btrfs_extent_item_v0))) {
>  		btrfs_print_v0_err(eb->fs_info);
>  		btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
>  		return -EINVAL;
> @@ -3742,7 +3742,7 @@ int add_data_references(struct reloc_control *rc,
>  					      struct btrfs_extent_data_ref);
>  			ret = find_data_references(rc, extent_key,
>  						   eb, dref, blocks);
> -		} else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
> +		} else if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
>  			btrfs_print_v0_err(eb->fs_info);
>  			btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
>  			ret = -EINVAL;
> @@ -3984,7 +3984,7 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
>  			flags = btrfs_extent_flags(path->nodes[0], ei);
>  			ret = check_extent_flags(flags);
>  			BUG_ON(ret);
> -		} else if (item_size == sizeof(struct btrfs_extent_item_v0)) {
> +		} else if (unlikely(item_size == sizeof(struct btrfs_extent_item_v0))) {
>  			err = -EINVAL;
>  			btrfs_print_v0_err(trans->fs_info);
>  			btrfs_abort_transaction(trans, err);
>