Re: [PATCH v3 3/3] fs: use kmem_cache_create_rcu()

[Vlastimil Babka <vbabka@suse.cz>]

On 8/28/24 12:56, Christian Brauner wrote:
> Switch to the new kmem_cache_create_rcu() helper which allows us to use
> a custom free pointer offset avoiding the need to have an external free
> pointer which would grow struct file behind our backs.
> 
> Signed-off-by: Christian Brauner <brauner@kernel.org>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  fs/file_table.c    | 6 +++---
>  include/linux/fs.h | 2 ++
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 694199a1a966..83d5ac1fadc0 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -514,9 +514,9 @@ EXPORT_SYMBOL(__fput_sync);
>  
>  void __init files_init(void)
>  {
> -	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
> -				SLAB_TYPESAFE_BY_RCU | SLAB_HWCACHE_ALIGN |
> -				SLAB_PANIC | SLAB_ACCOUNT, NULL);
> +	filp_cachep = kmem_cache_create_rcu("filp", sizeof(struct file),
> +				offsetof(struct file, f_freeptr),
> +				SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
>  	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
>  }
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 61097a9cf317..5ca83e87adef 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1026,6 +1026,7 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
>   * @f_task_work: task work entry point
>   * @f_llist: work queue entrypoint
>   * @f_ra: file's readahead state
> + * @f_freeptr: Pointer used by SLAB_TYPESAFE_BY_RCU file cache (don't touch.)
>   */
>  struct file {
>  	atomic_long_t			f_count;
> @@ -1057,6 +1058,7 @@ struct file {
>  		struct callback_head	f_task_work;
>  		struct llist_node	f_llist;
>  		struct file_ra_state	f_ra;
> +		freeptr_t		f_freeptr;
>  	};
>  	/* --- cacheline 3 boundary (192 bytes) --- */
>  } __randomize_layout
>