Re: [PATCH v5 3/5] mm/readahead: Make space in struct file_ra_state

[Christian Brauner <brauner@kernel.org>]

On Mon, Jun 09, 2025 at 10:27:25AM +0100, Ryan Roberts wrote:
> We need to be able to store the preferred folio order associated with a
> readahead request in the struct file_ra_state so that we can more
> accurately increase the order across subsequent readahead requests. But
> struct file_ra_state is per-struct file, so we don't really want to
> increase it's size.
> 
> mmap_miss is currently 32 bits but it is only counted up to 10 *
> MMAP_LOTSAMISS, which is currently defined as 1000. So 16 bits should be
> plenty. Redefine it to unsigned short, making room for order as unsigned
> short in follow up commit.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  include/linux/fs.h |  2 +-
>  mm/filemap.c       | 11 ++++++-----
>  2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 05abdabe9db7..87e7d5790e43 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1052,7 +1052,7 @@ struct file_ra_state {
>  	unsigned int size;
>  	unsigned int async_size;
>  	unsigned int ra_pages;
> -	unsigned int mmap_miss;
> +	unsigned short mmap_miss;

Thanks for not making struct file grow!