Re: [PATCH v5 17/19] mm: memcg/slab: use a single set of kmem_caches for all allocations

[Vlastimil Babka]

On 5/28/20 12:34 AM, Roman Gushchin wrote:
> diff --git a/mm/slab.h b/mm/slab.h
> index c49a863adb63..57b425d623e5 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
...
> @@ -526,8 +430,7 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
>  	 * When kmemcg is not being used, both assignments should return the
>  	 * same value. but we don't want to pay the assignment price in that
>  	 * case. If it is not compiled in, the compiler should be smart enough
> -	 * to not do even the assignment. In that case, slab_equal_or_root
> -	 * will also be a constant.
> +	 * to not do even the assignment.
>  	 */
>  	if (!memcg_kmem_enabled() &&

Just realized that this test can go away - we don't have to call virt_to_cache()
due to kmemcg if there is just a single cache.

>  	    !IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
> @@ -535,7 +438,7 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
>  		return s;
>  
>  	cachep = virt_to_cache(x);
> -	WARN_ONCE(cachep && !slab_equal_or_root(cachep, s),
> +	WARN_ONCE(cachep && cachep != s,
>  		  "%s: Wrong slab cache. %s but object is from %s\n",
>  		  __func__, s->name, cachep->name);
>  	return cachep;