mm: memcontrol: remove page_memcg()

The page_memcg() only called by mod_memcg_page_state(), so squash it to
cleanup page_memcg().

Link: https://lkml.kernel.org/r/20240524014950.187805-1-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -443,11 +443,6 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
 	return __folio_memcg(folio);
 }
 
-static inline struct mem_cgroup *page_memcg(struct page *page)
-{
-	return folio_memcg(page_folio(page));
-}
-
 /**
  * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
  * @folio: Pointer to the folio.
@@ -1014,7 +1009,7 @@ static inline void mod_memcg_page_state(struct page *page,
 		return;
 
 	rcu_read_lock();
-	memcg = page_memcg(page);
+	memcg = folio_memcg(page_folio(page));
 	if (memcg)
 		mod_memcg_state(memcg, idx, val);
 	rcu_read_unlock();
@@ -1133,11 +1128,6 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
 	return NULL;
 }
 
-static inline struct mem_cgroup *page_memcg(struct page *page)
-{
-	return NULL;
-}
-
 static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
 {
 	WARN_ON_ONCE(!rcu_read_lock_held());
@@ -1636,7 +1626,7 @@ static inline void unlock_page_lruvec_irqrestore(struct lruvec *lruvec,
 	spin_unlock_irqrestore(&lruvec->lru_lock, flags);
 }
 
-/* Test requires a stable page->memcg binding, see page_memcg() */
+/* Test requires a stable folio->memcg binding, see folio_memcg() */
 static inline bool folio_matches_lruvec(struct folio *folio,
 		struct lruvec *lruvec)
 {

mm/memcontrol.c

@@ -3807,7 +3807,7 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 #endif /* CONFIG_MEMCG_KMEM */
 
 /*
- * Because page_memcg(head) is not set on tails, set it now.
+ * Because folio_memcg(head) is not set on tails, set it now.
  */
 void split_page_memcg(struct page *head, int old_order, int new_order)
 {