mm: simplify split_page_memcg()

The last argument to split_page_memcg() is now always 0, so remove it,
effectively reverting commit b879138.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: Shakeel Butt <[email protected]>
Acked-by: Zi Yan <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

include/linux/memcontrol.h

@@ -1038,7 +1038,7 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
 	rcu_read_unlock();
 }
 
-void split_page_memcg(struct page *head, int old_order, int new_order);
+void split_page_memcg(struct page *first, unsigned order);
 void folio_split_memcg_refs(struct folio *folio, unsigned old_order,
 		unsigned new_order);
 
@@ -1461,7 +1461,7 @@ void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx)
 {
 }
 
-static inline void split_page_memcg(struct page *head, int old_order, int new_order)
+static inline void split_page_memcg(struct page *first, unsigned order)
 {
 }
 

mm/memcontrol.c

@@ -3066,22 +3066,21 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 }
 
 /*
- * Because folio_memcg(head) is not set on tails, set it now.
+ * The objcg is only set on the first page, so transfer it to all the
+ * other pages.
  */
-void split_page_memcg(struct page *head, int old_order, int new_order)
+void split_page_memcg(struct page *first, unsigned order)
 {
-	struct folio *folio = page_folio(head);
-	int i;
-	unsigned int old_nr = 1 << old_order;
-	unsigned int new_nr = 1 << new_order;
+	struct folio *folio = page_folio(first);
+	unsigned int i, nr = 1 << order;
 
 	if (mem_cgroup_disabled() || !folio_memcg_charged(folio))
 		return;
 
-	for (i = new_nr; i < old_nr; i += new_nr)
+	for (i = 1; i < nr; i++)
 		folio_page(folio, i)->memcg_data = folio->memcg_data;
 
-	obj_cgroup_get_many(__folio_objcg(folio), old_nr / new_nr - 1);
+	obj_cgroup_get_many(__folio_objcg(folio), nr - 1);
 }
 
 void folio_split_memcg_refs(struct folio *folio, unsigned old_order,

mm/page_alloc.c

@@ -2778,7 +2778,7 @@ void split_page(struct page *page, unsigned int order)
 		set_page_refcounted(page + i);
 	split_page_owner(page, order, 0);
 	pgalloc_tag_split(page_folio(page), order, 0);
-	split_page_memcg(page, order, 0);
+	split_page_memcg(page, order);
 }
 EXPORT_SYMBOL_GPL(split_page);
 
@@ -4992,7 +4992,7 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
 
 		split_page_owner(page, order, 0);
 		pgalloc_tag_split(page_folio(page), order, 0);
-		split_page_memcg(page, order, 0);
+		split_page_memcg(page, order);
 		while (page < --last)
 			set_page_refcounted(last);