mm: kmem: reimplement get_obj_cgroup_from_current()

Reimplement get_obj_cgroup_from_current() using current_obj_cgroup(). 
get_obj_cgroup_from_current() and current_obj_cgroup() share 80% of the
code, so the new implementation is almost trivial.

get_obj_cgroup_from_current() is a convenient function used by the
bpf subsystem, so there is no reason to get rid of it completely.

Link: https://lkml.kernel.org/r/20231019225346.1822282-7-roman.gushchin@linux.devSigned-off-by: Roman Gushchin (Cruise) <roman.gushchin@linux.dev>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Shakeel Butt <shakeelb@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -1805,9 +1805,18 @@ void __memcg_kmem_uncharge_page(struct page *page, int order);
  * needs to be used outside of the local scope.
  */
 struct obj_cgroup *current_obj_cgroup(void);
-struct obj_cgroup *get_obj_cgroup_from_current(void);
 struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio);
 
+static inline struct obj_cgroup *get_obj_cgroup_from_current(void)
+{
+	struct obj_cgroup *objcg = current_obj_cgroup();
+
+	if (objcg)
+		obj_cgroup_get(objcg);
+
+	return objcg;
+}
+
 int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size);
 void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size);
 

mm/memcontrol.c

@@ -3138,38 +3138,6 @@ static struct obj_cgroup *current_objcg_update(void)
 	return objcg;
 }
 
-__always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
-{
-	struct mem_cgroup *memcg;
-	struct obj_cgroup *objcg;
-
-	if (in_task()) {
-		memcg = current->active_memcg;
-		if (unlikely(memcg))
-			goto from_memcg;
-
-		objcg = READ_ONCE(current->objcg);
-		if (unlikely((unsigned long)objcg & CURRENT_OBJCG_UPDATE_FLAG))
-			objcg = current_objcg_update();
-
-		if (objcg) {
-			obj_cgroup_get(objcg);
-			return objcg;
-		}
-	} else {
-		memcg = this_cpu_read(int_active_memcg);
-		if (unlikely(memcg))
-			goto from_memcg;
-	}
-	return NULL;
-
-from_memcg:
-	rcu_read_lock();
-	objcg = __get_obj_cgroup_from_memcg(memcg);
-	rcu_read_unlock();
-	return objcg;
-}
-
 __always_inline struct obj_cgroup *current_obj_cgroup(void)
 {
 	struct mem_cgroup *memcg;