Re: [PATCH v2] fs: pack fields `i_state` and `i_fsnotify_mask`

[David Laight <david.laight.linux@gmail.com>]

On Fri, 13 Nov 2026 12:44:26 +0100
Max Kellermann <max.kellermann@ionos.com> wrote:

I'd use a different workd than 'pack', made me think of __packed.

> Both were 32 bit fields followed by a 32 bit hole.  This reduces size
> of `struct inode` by 8 bytes.
> 
> Moving `i_fsnotify_marks` there as well so they can be in the same
> cacheline.
> 
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
> ---
> v1->v2: move `i_fsnotify_marks` up as well because "should better be
>   in the same cacheline because these two are accessed on some
>   performance sensitive paths" (Jan Kara)
> ---
>  include/linux/fs.h | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 5b3a100aba77..fec047cc3327 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -813,7 +813,13 @@ struct inode {
>  
>  	/* Misc */
>  	struct inode_state_flags i_state;
> -	/* 32-bit hole */
> +
> +#ifdef CONFIG_FSNOTIFY
> +	__u32			i_fsnotify_mask; /* all events this inode cares about */
> +
> +	struct fsnotify_mark_connector __rcu	*i_fsnotify_marks;

#else
	/* 32-bit hole */
??

David

> +#endif
> +
>  	struct rw_semaphore	i_rwsem;
>  
>  	/* Timestamp for writeback list ordering and age checks (jiffies). */
> @@ -863,13 +869,6 @@ struct inode {
>  		unsigned		i_dir_seq;
>  	};
>  
> -
> -#ifdef CONFIG_FSNOTIFY
> -	__u32			i_fsnotify_mask; /* all events this inode cares about */
> -	/* 32-bit hole reserved for expanding i_fsnotify_mask */
> -	struct fsnotify_mark_connector __rcu	*i_fsnotify_marks;
> -#endif
> -
>  	void			*i_private; /* fs or device private pointer */
>  } __randomize_layout;
>