[PATCH 1/6] Revert "memcg: remove mem_cgroup_uncharge_list()"

[Usama Arif <usamaarif642@gmail.com>]

mem_cgroup_uncharge_list will be needed in a later patch for an
optimization to free zapped tail pages when splitting isolated thp.

Signed-off-by: Usama Arif <usamaarif642@gmail.com>
---
 include/linux/memcontrol.h | 12 ++++++++++++
 mm/memcontrol.c            | 19 +++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 07eadf7ecbba..cbaf0ea1b217 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -713,6 +713,14 @@ static inline void mem_cgroup_uncharge(struct folio *folio)
 	__mem_cgroup_uncharge(folio);
 }
 
+void __mem_cgroup_uncharge_list(struct list_head *page_list);
+static inline void mem_cgroup_uncharge_list(struct list_head *page_list)
+{
+	if (mem_cgroup_disabled())
+		return;
+	__mem_cgroup_uncharge_list(page_list);
+}
+
 void __mem_cgroup_uncharge_folios(struct folio_batch *folios);
 static inline void mem_cgroup_uncharge_folios(struct folio_batch *folios)
 {
@@ -1203,6 +1211,10 @@ static inline void mem_cgroup_uncharge(struct folio *folio)
 {
 }
 
+static inline void mem_cgroup_uncharge_list(struct list_head *page_list)
+{
+}
+
 static inline void mem_cgroup_uncharge_folios(struct folio_batch *folios)
 {
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9b3ef3a70833..f568b9594c2b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4717,6 +4717,25 @@ void __mem_cgroup_uncharge(struct folio *folio)
 	uncharge_batch(&ug);
 }
 
+/**
+ * __mem_cgroup_uncharge_list - uncharge a list of page
+ * @page_list: list of pages to uncharge
+ *
+ * Uncharge a list of pages previously charged with
+ * __mem_cgroup_charge().
+ */
+void __mem_cgroup_uncharge_list(struct list_head *page_list)
+{
+	struct uncharge_gather ug;
+	struct folio *folio;
+
+	uncharge_gather_clear(&ug);
+	list_for_each_entry(folio, page_list, lru)
+		uncharge_folio(folio, &ug);
+	if (ug.memcg)
+		uncharge_batch(&ug);
+}
+
 void __mem_cgroup_uncharge_folios(struct folio_batch *folios)
 {
 	struct uncharge_gather ug;
-- 
2.43.0