mm: kmem: remove mem_cgroup_from_obj()

There is no user of mem_cgroup_from_obj(), remove it.

Link: https://lkml.kernel.org/r/20240718091821.44740-1-songmuchun@bytedance.comSigned-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -1717,7 +1717,6 @@ static inline int memcg_kmem_id(struct mem_cgroup *memcg)
 	return memcg ? memcg->kmemcg_id : -1;
 }
 
-struct mem_cgroup *mem_cgroup_from_obj(void *p);
 struct mem_cgroup *mem_cgroup_from_slab_obj(void *p);
 
 static inline void count_objcg_event(struct obj_cgroup *objcg,
@@ -1780,11 +1779,6 @@ static inline int memcg_kmem_id(struct mem_cgroup *memcg)
 	return -1;
 }
 
-static inline struct mem_cgroup *mem_cgroup_from_obj(void *p)
-{
-	return NULL;
-}
-
 static inline struct mem_cgroup *mem_cgroup_from_slab_obj(void *p)
 {
 	return NULL;

mm/memcontrol.c

@@ -2446,37 +2446,7 @@ struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p)
 
 /*
  * Returns a pointer to the memory cgroup to which the kernel object is charged.
- *
- * A passed kernel object can be a slab object, vmalloc object or a generic
- * kernel page, so different mechanisms for getting the memory cgroup pointer
- * should be used.
- *
- * In certain cases (e.g. kernel stacks or large kmallocs with SLUB) the caller
- * can not know for sure how the kernel object is implemented.
- * mem_cgroup_from_obj() can be safely used in such cases.
- *
- * The caller must ensure the memcg lifetime, e.g. by taking rcu_read_lock(),
- * cgroup_mutex, etc.
- */
-struct mem_cgroup *mem_cgroup_from_obj(void *p)
-{
-	struct folio *folio;
-
-	if (mem_cgroup_disabled())
-		return NULL;
-
-	if (unlikely(is_vmalloc_addr(p)))
-		folio = page_folio(vmalloc_to_page(p));
-	else
-		folio = virt_to_folio(p);
-
-	return mem_cgroup_from_obj_folio(folio, p);
-}
-
-/*
- * Returns a pointer to the memory cgroup to which the kernel object is charged.
- * Similar to mem_cgroup_from_obj(), but faster and not suitable for objects,
- * allocated using vmalloc().
+ * It is not suitable for objects allocated using vmalloc().
  *
  * A passed kernel object must be a slab object or a generic kernel page.
  *