mm: remove references to folio in __memcg_kmem_uncharge_page()

This use of folios is misleading because these pages are not part of
a folio.  Remove an unnecessary call to page_folio(), saving 58 bytes
of text in a Debian kernel build.

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: Roman Gushchin <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

mm/memcontrol.c

@@ -2726,16 +2726,14 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
  */
 void __memcg_kmem_uncharge_page(struct page *page, int order)
 {
-	struct folio *folio = page_folio(page);
-	struct obj_cgroup *objcg;
+	struct obj_cgroup *objcg = page_objcg(page);
 	unsigned int nr_pages = 1 << order;
 
-	if (!folio_memcg_kmem(folio))
+	if (!objcg)
 		return;
 
-	objcg = __folio_objcg(folio);
 	obj_cgroup_uncharge_pages(objcg, nr_pages);
-	folio->memcg_data = 0;
+	page->memcg_data = 0;
 	obj_cgroup_put(objcg);
 }