Re: [PATCH 1/2] btrfs: relocation: Cleanup while() loop using for()

[Nikolay Borisov <nborisov@suse.com>]

On 21.09.2018 09:45, Qu Wenruo wrote:
> And add one line comment explaining what we're doing for each loop.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/relocation.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 8783a1776540..d7f5a11dde20 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -2997,27 +2997,25 @@ int relocate_tree_blocks(struct btrfs_trans_handle *trans,
>  		goto out_free_blocks;
>  	}
>  
> -	rb_node = rb_first(blocks);
> -	while (rb_node) {
> +	/* Kick in readahead for tree blocks with missing keys */
> +	for (rb_node = rb_first(blocks); rb_node; rb_node = rb_next(rb_node)) {

FYI there is already a rbtree_postorder_for_each_entry_safe functino
which allows to iterate the rb tree in post order. It provides stronger
guarantees than you actually need (namely the _safe ) but in any case it
will allows you to get rid of the "block = " line as well as the
"rb_node =" line. This will remove all superfluous code that's needed to
handle the iteration.

>  		block = rb_entry(rb_node, struct tree_block, rb_node);
>  		if (!block->key_ready)
>  			readahead_tree_block(fs_info, block->bytenr);
> -		rb_node = rb_next(rb_node);
>  	}
>  
> -	rb_node = rb_first(blocks);
> -	while (rb_node) {
> +	/* Get first keys */
> +	for (rb_node = rb_first(blocks); rb_node; rb_node = rb_next(rb_node)) {
>  		block = rb_entry(rb_node, struct tree_block, rb_node);
>  		if (!block->key_ready) {
>  			err = get_tree_block_key(fs_info, block);
>  			if (err)
>  				goto out_free_path;
>  		}
> -		rb_node = rb_next(rb_node);
>  	}
>  
> -	rb_node = rb_first(blocks);
> -	while (rb_node) {
> +	/* Do tree relocation */
> +	for (rb_node = rb_first(blocks); rb_node; rb_node = rb_next(rb_node)) {
>  		block = rb_entry(rb_node, struct tree_block, rb_node);
>  
>  		node = build_backref_tree(rc, &block->key,
> @@ -3034,7 +3032,6 @@ int relocate_tree_blocks(struct btrfs_trans_handle *trans,
>  				err = ret;
>  			goto out;
>  		}
> -		rb_node = rb_next(rb_node);
>  	}
>  out:
>  	err = finish_pending_nodes(trans, rc, path, err);
>