Re: [PATCH RFC 05/12] mm/slab: abstract slabobj_ext.objcg access

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Jul 16, 2026 at 6:58 AM Vlastimil Babka (SUSE)
<vbabka@kernel.org> wrote:
>
> On 7/16/26 03:27, Suren Baghdasaryan wrote:
> > On Wed, Jul 15, 2026 at 3:11 AM Vlastimil Babka (SUSE)
> > <vbabka@kernel.org> wrote:
> >> --- a/mm/slab.h
> >> +++ b/mm/slab.h
> >> @@ -555,7 +555,7 @@ static inline bool need_kmalloc_no_objext(void)
> >>   */
> >>  struct slabobj_ext {
> >>  #ifdef CONFIG_MEMCG
> >> -       struct obj_cgroup *objcg;
> >> +       struct obj_cgroup *_objcg;
> >>  #endif
> >>  #ifdef CONFIG_MEM_ALLOC_PROFILING
> >>         union codetag_ref ref;
> >> @@ -661,6 +661,13 @@ slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
> >>         return kasan_reset_tag(obj_ext);
> >>  }
> >>
> >> +#ifdef CONFIG_MEMCG
> >> +static inline struct obj_cgroup **slab_obj_ext_objcgp(struct slabobj_ext *obj_ext)
> >
> > I understand why you need to return obj_cgroup** but maybe instead we
> > can have a separate setter function and just return a pointer here?
>
> Yeah I rewrote it now and it looks better. Thanks! It ended up like this due
> to some previous attempt I made.
>
> > That would also help catch cases when someone wants to set
> > obj_ext._objcg that was optimized away (for that the setter would need
> > an additional parameter to identify whether we allocated optimized
> > objext vector).
>
> It would need passing the slab parameter to assert
> slab_obj_ext_has_codetag() in debug mode. I don't think it's worth it given
> the get/set is only called from few specialized places.

Sounds good.

>
> >
> >> +{
> >> +       return &obj_ext->_objcg;
> >> +}
> >> +#endif
> >> +
> >>  int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
> >>                         gfp_t gfp, unsigned int alloc_flags);
> >>
> >> diff --git a/mm/slub.c b/mm/slub.c
> >> index 5e3f53bcd0d3..48e10198a3ce 100644
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -2523,7 +2523,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
> >>         if (obj_exts) {
> >>                 get_slab_obj_exts(obj_exts);
> >>                 obj_ext = slab_obj_ext(s, slab, obj_exts, p);
> >> -               if (unlikely(obj_ext->objcg)) {
> >> +               if (unlikely(*slab_obj_ext_objcgp(obj_ext))) {
> >>                         put_slab_obj_exts(obj_exts);
> >>                         return true;
> >>                 }
> >>
> >> --
> >> 2.55.0
> >>
>