Re: [PATCH 1/2] mm/slab: restore the rcutree. prefix of the kvfree_rcu parameters

[Harry Yoo <harry@kernel.org>]

On Wed, Oct 28, 2026 at 09:46:46PM +0800, Zhan Xusheng wrote:
> From: Zhan Xusheng <zhanxusheng@xiaomi.com>
> 
> The move of kvfree_rcu() to mm/slab_common.c dropped the "rcutree."
> MODULE_PARAM_PREFIX, so rcu_min_cached_objs and
> rcu_delay_page_cache_fill_msec became slab_common.* and the documented
> rcutree.* names are silently ignored.  Restore the prefix; the
> slab_common.* names, never documented, stop working.
> 
> Fixes: bbe658d65802 ("mm/slab: Move kvfree_rcu() into SLAB")

We should add:

Cc: stable@vger.kernel.org

This is a functional regression and in MM we don't automatically
backport fixes to -stable unless without this tag.

> Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
> ---
>  mm/slab_common.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 01c64ef661e7..3729aa7a6156 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1373,6 +1373,10 @@ void __init kvfree_rcu_init(void)
>   * per-CPU. Object size is equal to one page. This value
>   * can be changed at boot time.
>   */
> +/* These used to be rcutree parameters; keep their documented names. */
> +#undef MODULE_PARAM_PREFIX
> +#define MODULE_PARAM_PREFIX "rcutree."

This should be moved to before "This rcu parameter is
runtime-read-only ..." part?

And perhaps let's rephrase the comment, something like:

/* Keep the prefix inherited from RCU */

With that adjusted, otherwise looks good to me, so:
Reviewed-by: Harry Yoo (Meta) <harry@kernel.org>

-- 
Cheers,
Harry / Hyeonggon