Re: [PATCH 09/15] btrfs: shrink the size of struct btrfs_delayed_item

[David Sterba <dsterba@suse.cz>]

On Wed, Aug 17, 2022 at 12:22:42PM +0100, fdmanana@kernel.org wrote:
>  	}
>  
>  	item->index = index;
> -	item->ins_or_del = BTRFS_DELAYED_DELETION_ITEM;
>  
>  	ret = btrfs_delayed_item_reserve_metadata(trans, item);
>  	/*
> diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h
> index fd6fe785f748..729d352ca8a1 100644
> --- a/fs/btrfs/delayed-inode.h
> +++ b/fs/btrfs/delayed-inode.h
> @@ -16,9 +16,10 @@
>  #include <linux/refcount.h>
>  #include "ctree.h"
>  
> -/* types of the delayed item */
> -#define BTRFS_DELAYED_INSERTION_ITEM	1
> -#define BTRFS_DELAYED_DELETION_ITEM	2
> +enum btrfs_delayed_item_type {
> +	BTRFS_DELAYED_INSERTION_ITEM,
> +	BTRFS_DELAYED_DELETION_ITEM
> +};
>  
>  struct btrfs_delayed_root {
>  	spinlock_t lock;
> @@ -80,8 +81,9 @@ struct btrfs_delayed_item {
>  	u64 bytes_reserved;
>  	struct btrfs_delayed_node *delayed_node;
>  	refcount_t refs;
> -	int ins_or_del;
> -	u32 data_len;
> +	enum btrfs_delayed_item_type type:1;

Bit fields next to atomicly accessed variables could be problemantic on
architectures without safe unaligned access. Either this can be :8 or
moved after 'key' where's a 7 byte hole.