On Tue, 27 Jul 2021, Goldwyn Rodrigues wrote:
> Simplification.
>
> file_ra_state_init() take struct address_space *, just to use inode
> pointer by dereferencing from mapping->host.
>
> The callers also derive mapping either by file->f_mapping, or
> even file->f_mapping->host->i_mapping.
>
> Change file_ra_state_init() to accept struct inode * to reduce pointer
> dereferencing, both in the callee and the caller.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> ---
....
> diff --git a/mm/readahead.c b/mm/readahead.c
> index d589f147f4c2..3541941df5e7 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -31,9 +31,9 @@
> * memset *ra to zero.
> */
> void
> -file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
> +file_ra_state_init(struct file_ra_state *ra, struct inode *inode)
> {
> - ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
> + ra->ra_pages = inode_to_bdi(inode)->ra_pages;
> ra->prev_pos = -1;
I think this patch can be made OK by adding:
if (unlikely(inode->i_mapping != &inode->i_data))
inode = inode->i_mapping->host;
The "unlikely" is mostly for documentation.
Loading "inode->i_mapping" is nearly free as that cache line needs to be
loaded to get i_sb, which inode_to_bdi() needs. Calculating &->i_data
is trivial. So this adds minimal cost, and preserves correctness.
NeilBrown
> }
> EXPORT_SYMBOL_GPL(file_ra_state_init);
> --
> 2.32.0
>
>
> --
> Goldwyn
>
>
