[PATCH v3 11/25] mm/memcg: Add folio_memcg, lock_folio_memcg and unlock_folio_memcg

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

The memcontrol code already assumes that page_memcg() will be called
with a non-tail page, so make that more natural by wrapping it with a
folio API.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 include/linux/memcontrol.h | 16 ++++++++++++++++
 mm/memcontrol.c            | 36 ++++++++++++++++++++++++------------
 2 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7a38a1517a05..89aaa22506e6 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -383,6 +383,11 @@ static inline struct mem_cgroup *page_memcg(struct page *page)
 	return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
 }
 
+static inline struct mem_cgroup *folio_memcg(struct folio *folio)
+{
+	return page_memcg(&folio->page);
+}
+
 /*
  * page_memcg_rcu - locklessly get the memory cgroup associated with a page
  * @page: a pointer to the page struct
@@ -869,8 +874,10 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg);
 extern bool cgroup_memory_noswap;
 #endif
 
+struct mem_cgroup *lock_folio_memcg(struct folio *folio);
 struct mem_cgroup *lock_page_memcg(struct page *page);
 void __unlock_page_memcg(struct mem_cgroup *memcg);
+void unlock_folio_memcg(struct folio *folio);
 void unlock_page_memcg(struct page *page);
 
 /*
@@ -1298,6 +1305,11 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
 {
 }
 
+static inline struct mem_cgroup *lock_folio_memcg(struct folio *folio)
+{
+	return NULL;
+}
+
 static inline struct mem_cgroup *lock_page_memcg(struct page *page)
 {
 	return NULL;
@@ -1307,6 +1319,10 @@ static inline void __unlock_page_memcg(struct mem_cgroup *memcg)
 {
 }
 
+static inline void unlock_folio_memcg(struct folio *folio)
+{
+}
+
 static inline void unlock_page_memcg(struct page *page)
 {
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ed5cc78a8dbf..c3c0c8124b09 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2139,19 +2139,18 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
 }
 
 /**
- * lock_page_memcg - lock a page and memcg binding
- * @page: the page
+ * lock_folio_memcg - lock a folio and memcg binding
+ * @folio: the folio
  *
- * This function protects unlocked LRU pages from being moved to
+ * This function protects unlocked LRU folios from being moved to
  * another cgroup.
  *
  * It ensures lifetime of the returned memcg. Caller is responsible
- * for the lifetime of the page; __unlock_page_memcg() is available
- * when @page might get freed inside the locked section.
+ * for the lifetime of the folio; __unlock_folio_memcg() is available
+ * when @folio might get freed inside the locked section.
  */
-struct mem_cgroup *lock_page_memcg(struct page *page)
+struct mem_cgroup *lock_folio_memcg(struct folio *folio)
 {
-	struct page *head = compound_head(page); /* rmap on tail pages */
 	struct mem_cgroup *memcg;
 	unsigned long flags;
 
@@ -2171,7 +2170,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
 	if (mem_cgroup_disabled())
 		return NULL;
 again:
-	memcg = page_memcg(head);
+	memcg = folio_memcg(folio);
 	if (unlikely(!memcg))
 		return NULL;
 
@@ -2185,7 +2184,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
 		return memcg;
 
 	spin_lock_irqsave(&memcg->move_lock, flags);
-	if (memcg != page_memcg(head)) {
+	if (memcg != folio_memcg(folio)) {
 		spin_unlock_irqrestore(&memcg->move_lock, flags);
 		goto again;
 	}
@@ -2200,6 +2199,12 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
 
 	return memcg;
 }
+EXPORT_SYMBOL(lock_folio_memcg);
+
+struct mem_cgroup *lock_page_memcg(struct page *page)
+{
+	return lock_folio_memcg(page_folio(page));
+}
 EXPORT_SYMBOL(lock_page_memcg);
 
 /**
@@ -2222,15 +2227,22 @@ void __unlock_page_memcg(struct mem_cgroup *memcg)
 	rcu_read_unlock();
 }
 
+/**
+ * unlock_folio_memcg - unlock a folio and memcg binding
+ * @folio: the folio
+ */
+void unlock_folio_memcg(struct folio *folio)
+{
+	__unlock_page_memcg(folio_memcg(folio));
+}
+
 /**
  * unlock_page_memcg - unlock a page and memcg binding
  * @page: the page
  */
 void unlock_page_memcg(struct page *page)
 {
-	struct page *head = compound_head(page);
-
-	__unlock_page_memcg(page_memcg(head));
+	unlock_folio_memcg(page_folio(page));
 }
 EXPORT_SYMBOL(unlock_page_memcg);
 
-- 
2.29.2