Re: [PATCH v2 12/13] mm/slab: add cache_ and slab_needs_objcg() helpers

[Hao Li <hao.li@linux.dev>]

On Thu, Jul 23, 2026 at 11:30:49AM +0200, Vlastimil Babka (SUSE) wrote:
> On 7/23/26 11:25, Hao Li wrote:
> > On Mon, Jul 20, 2026 at 04:16:26PM +0200, Vlastimil Babka (SUSE) wrote:
> >> @@ -359,6 +359,13 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
> >>  		goto out_unlock;
> >>  	}
> >>  
> >> +	/*
> >> +	 * For now we assume any cache can be used with __GFP_ACCOUNT and thus
> >> +	 * may need to store objcg pointers for objects
> >> +	 */
> >> +	if (!mem_cgroup_kmem_disabled())
> >> +		flags |= SLAB_MAY_ACCOUNT;
> > 
> > if memcg itself is disabled via `cgroup_disable`, mem_cgroup_kmem_disabled()
> > still return false, so maybe we can use:
> 
> Aha, but then shouldn't rather mem_cgroup_kmem_disabled() take that into
> account on its own?

Yeah, it's better to handle two cases in mem_cgroup_kmem_disabled!
This could also be a standalone patch, but including it to this patchset it totally
fine.

> 
> > if (!mem_cgroup_disabled() && !mem_cgroup_kmem_disabled())
> > 	flags |= SLAB_MAY_ACCOUNT;
> > 
> >> +
> >>  	/* Fail closed on bad usersize of useroffset values. */
> >>  	if (!IS_ENABLED(CONFIG_HARDENED_USERCOPY) ||
> >>  	    WARN_ON(!args->usersize && args->useroffset) ||
> >> @@ -984,11 +991,19 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type)
> >>  #endif
> >>  
> >>  	/*
> >> -	 * If CONFIG_MEMCG is enabled, disable cache merging for
> >> -	 * KMALLOC_NORMAL caches.
> >> +	 * If memcg_kmem is enabled and this is a KMALLOC_NORMAL cache and  not
> >> +	 * aliased with any other type, make sure it's never merged with any other
> >> +	 * cache.
> >> +	 *
> >> +	 * In other cases the kmalloc cache may end up being used for a
> >> +	 * __GFP_ACCOUNT allocation so mark it as such
> >>  	 */
> >> -	if (IS_ENABLED(CONFIG_MEMCG) && (type == KMALLOC_NORMAL))
> >> -		flags |= SLAB_NO_MERGE;
> >> +	if (!mem_cgroup_kmem_disabled()) {
> > 
> > the same as above
> > 
> > Others look good to me.
> > 
> > Reviewed-by: Hao Li <hao.li@linux.dev>
> 
> Thanks!
> 
> > 
> >> +		if (type == KMALLOC_NORMAL && KMALLOC_RECLAIM != KMALLOC_NORMAL)
> >> +			flags |= SLAB_NO_MERGE;
> >> +		else
> >> +			flags |= SLAB_MAY_ACCOUNT;
> >> +	}
> >>  
> >>  	if (minalign > ARCH_KMALLOC_MINALIGN) {
> >>  		aligned_size = ALIGN(aligned_size, minalign);
> >> diff --git a/mm/slub.c b/mm/slub.c
> >> index d78d3e50c877..30435e2509ea 100644
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -2557,7 +2557,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
> >>  	 * of slab_obj_exts being allocated from the same slab and thus the slab
> >>  	 * becoming effectively unfreeable.
> >>  	 */
> >> -	if (is_kmalloc_normal(s))
> >> +	if (!cache_needs_objcg(s))
> >>  		return true;
> >>  
> >>  	/* Ignore already charged objects. */
> >> @@ -3435,6 +3435,10 @@ static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags,
> >>  
> >>  	slab->objects = oo_objects(oo);
> >>  
> >> +#ifdef CONFIG_64BIT
> >> +	if (cache_needs_objcg(s))
> >> +		slab->obj_exts_needs_objcg = 1;
> >> +#endif
> >>  	slab->slab_cache = s;
> >>  
> >>  	kasan_poison_slab(slab);
> >> 
> >> -- 
> >> 2.55.0
> >> 
> > 
> 

-- 
Thanks,
Hao