On Tue, Jun 18, 2024 at 07:35:05PM GMT, Junchao Sun wrote:
> By reordering the elements in the struct file structure, we can
> reduce the padding needed on an x86_64 system by 8 bytes.
>
> Signed-off-by: Junchao Sun <sunjunchao2870@xxxxxxxxx>
> ---
> include/linux/fs.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 0283cf366c2a..9235b7a960d3 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -999,10 +999,10 @@ struct file {
> */
> spinlock_t f_lock;
> fmode_t f_mode;
> + unsigned int f_flags;
Iiuc, then this will push f_pos_lock into a new cache line whereas it's
explicitly optimized so that f_lock, f_mode, and f_pos_lock are all in
the same cache line.
You could play around with moving the union to the end of struct file.
