Re: [PATCH RFC 01/12] mm/slab: skip kfence objects in allocation profiling

On Wed, Jul 15, 2026 at 3:10 AM Vlastimil Babka (SUSE)
<[email protected]> wrote:
>
> struct kfence_metadata only has obj_exts with CONFIG_MEMCG.

I don't quite understand this statement. obj_exts are allocated when
either CONFIG_MEMCG or CONFIG_MEM_ALLOC_PROFILING is enabled.

> If it's
> enabled, it does also work for allocation profiling, but there's little
> value recording tags for KFENCE objects.

Unless we are leaking them, right?

> Furthermore it would complicate
> the upcoming changes, so just skip them in the slab hooks.

Ok, I can understand that. If we do this, we should document that
kfence objects are no longer tracked.

>
> Signed-off-by: Vlastimil Babka (SUSE) <[email protected]>
> ---
>  mm/slub.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 0337e60db5ac..a4be70d080fb 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2352,6 +2352,9 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
>         if (alloc_flags & SLAB_ALLOC_NO_RECURSE)
>                 return;
>
> +       if (is_kfence_address(object))
> +               return;
> +
>         slab = virt_to_slab(object);
>         obj_exts = prepare_slab_obj_exts_hook(s, slab, flags, alloc_flags, object);
>         /*
> @@ -2399,6 +2402,9 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
>         for (i = 0; i < objects; i++) {
>                 unsigned int off = obj_to_index(s, slab, p[i]);
>
> +               if (is_kfence_address(p[i]))
> +                       continue;
> +
>                 alloc_tag_sub(&slab_obj_ext(slab, obj_exts, off)->ref, s->size);
>         }
>         put_slab_obj_exts(obj_exts);
>
> --
> 2.55.0
>