linux-kernel - Re: [PATCH] mm: Remove reference to destructor in comment in calculate

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Message-ID: <aPdwcpe91TkdPZ2V@hyeyoo>
Date: Tue, 21 Oct 2025 20:38:24 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: William Kucharski <william.kucharski@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...two.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Paul Mundt <lethal@...ux-sh.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Remove reference to destructor in comment in
 calculate_sizes()

On Tue, Oct 21, 2025 at 05:00:04AM -0600, William Kucharski wrote:
> The commit that removed support for destructors from kmem_cache_alloc()
> never removed the comment regarding destructors in the explanation
> of the possible relocation of the free pointer in calculate_sizes().

Hi William,

I've been trying to reintroduce slab destructor (which hasn't been reposted
for a while...) [1]

[1] https://lore.kernel.org/linux-mm/20250424080755.272925-1-harry.yoo@oracle.com

I haven't had enough time to get back to it yet, but I haven't given up
on it either... so let us keep the comment? Otherwise I need add that
comment back as part of my series.

-- 
Cheers,
Harry / Hyeonggon

> Fixes: 20c2df83d25c ("mm: Remove slab destructors from kmem_cache_create().")


> Signed-off-by: William Kucharski <william.kucharski@...cle.com>
> ---
>  mm/slub.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index a8fcc7e6f25a..09cbbe923a05 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -7875,11 +7875,11 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
>  		 * permitted to overwrite the first word of the object on
>  		 * kmem_cache_free.
>  		 *
> -		 * This is the case if we do RCU, have a constructor or
> -		 * destructor, are poisoning the objects, or are
> -		 * redzoning an object smaller than sizeof(void *) or are
> -		 * redzoning an object with slub_debug_orig_size() enabled,
> -		 * in which case the right redzone may be extended.
> +		 * This is the case if we do RCU, have a constructor, are
> +		 * poisoning the objects, or are redzoning an object smaller
> +		 * than sizeof(void *) or are redzoning an object with
> +		 * slub_debug_orig_size() enabled, in which case the right
> +		 * redzone may be extended.
>  		 *
>  		 * The assumption that s->offset >= s->inuse means free
>  		 * pointer is outside of the object is used in the