mm: separate folio_split_memcg_refs() from split_page_memcg()

Patch series "Minor memcg cleanups & prep for memdescs", v2.

Separate the handling of accounted folios and GFP_ACCOUNT pages for easier
to understand code.  For more detail, see
https://lore.kernel.org/linux-mm/[email protected]/


This patch (of 5):

Folios always use memcg_data to refer to the mem_cgroup while pages
allocated with GFP_ACCOUNT have a pointer to the obj_cgroup.  Since the
caller already knows what it has, split the function into two and then we
don't need to check.

Move the assignment of split folio memcg_data to the point where we set up
the other parts of the new folio.  That leaves folio_split_memcg_refs()
just handling the memcg accounting.

Link: https://lkml.kernel.org/r/[email protected]
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: Matthew Wilcow (Oracle) <[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

@@ -1039,6 +1039,8 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
 }
 
 void split_page_memcg(struct page *head, int old_order, int new_order);
+void folio_split_memcg_refs(struct folio *folio, unsigned old_order,
+		unsigned new_order);
 
 static inline u64 cgroup_id_from_mm(struct mm_struct *mm)
 {
@@ -1463,6 +1465,11 @@ static inline void split_page_memcg(struct page *head, int old_order, int new_or
 {
 }
 
+static inline void folio_split_memcg_refs(struct folio *folio,
+		unsigned old_order, unsigned new_order)
+{
+}
+
 static inline u64 cgroup_id_from_mm(struct mm_struct *mm)
 {
 	return 0;

mm/huge_memory.c

@@ -3394,6 +3394,9 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
 			folio_set_young(new_folio);
 		if (folio_test_idle(folio))
 			folio_set_idle(new_folio);
+#ifdef CONFIG_MEMCG
+		new_folio->memcg_data = folio->memcg_data;
+#endif
 
 		folio_xchg_last_cpupid(new_folio, folio_last_cpupid(folio));
 	}
@@ -3525,18 +3528,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
 			}
 		}
 
-		/*
-		 * Reset any memcg data overlay in the tail pages.
-		 * folio_nr_pages() is unreliable until prep_compound_page()
-		 * was called again.
-		 */
-#ifdef NR_PAGES_IN_LARGE_FOLIO
-		folio->_nr_pages = 0;
-#endif
-
-
-		/* complete memcg works before add pages to LRU */
-		split_page_memcg(&folio->page, old_order, split_order);
+		folio_split_memcg_refs(folio, old_order, split_order);
 		split_page_owner(&folio->page, old_order, split_order);
 		pgalloc_tag_split(folio, old_order, split_order);
 

mm/memcontrol.c

@@ -3081,10 +3081,19 @@ void split_page_memcg(struct page *head, int old_order, int new_order)
 	for (i = new_nr; i < old_nr; i += new_nr)
 		folio_page(folio, i)->memcg_data = folio->memcg_data;
 
-	if (folio_memcg_kmem(folio))
-		obj_cgroup_get_many(__folio_objcg(folio), old_nr / new_nr - 1);
-	else
-		css_get_many(&folio_memcg(folio)->css, old_nr / new_nr - 1);
+	obj_cgroup_get_many(__folio_objcg(folio), old_nr / new_nr - 1);
+}
+
+void folio_split_memcg_refs(struct folio *folio, unsigned old_order,
+		unsigned new_order)
+{
+	unsigned new_refs;
+
+	if (mem_cgroup_disabled() || !folio_memcg_charged(folio))
+		return;
+
+	new_refs = (1 << (old_order - new_order)) - 1;
+	css_get_many(&__folio_memcg(folio)->css, new_refs);
 }
 
 unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)