[PATCH 1/5] mm: Separate folio_split_memcg() from split_page_memcg()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

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()
just handling the memcg accounting.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/memcontrol.h |  7 +++++++
 mm/huge_memory.c           | 16 ++++------------
 mm/memcontrol.c            | 17 +++++++++++++----
 3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 57664e2a8fb7..2b4246dc4284 100644
--- a/include/linux/memcontrol.h
+++ b/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(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(struct folio *folio, unsigned old_order,
+		unsigned new_order)
+{
+}
+
 static inline u64 cgroup_id_from_mm(struct mm_struct *mm)
 {
 	return 0;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 14b1963898a7..514db6a5eee7 100644
--- a/mm/huge_memory.c
+++ b/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(folio, old_order, split_order);
 		split_page_owner(&folio->page, old_order, split_order);
 		pgalloc_tag_split(folio, old_order, split_order);
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 87544df4c3b8..102109d0ee87 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3101,10 +3101,19 @@ 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(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)
-- 
2.47.2