mm/memcg: Add folio_memcg_lock() and folio_memcg_unlock()

These are the folio equivalents of lock_page_memcg() and
unlock_page_memcg().

lock_page_memcg() and unlock_page_memcg() have too many callers to be
easily replaced in a single patch, so reimplement them as wrappers for
now to be cleaned up later when enough callers have been converted to
use folios.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/memcontrol.h

@@ -978,6 +978,8 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg);
 extern bool cgroup_memory_noswap;
 #endif
 
+void folio_memcg_lock(struct folio *folio);
+void folio_memcg_unlock(struct folio *folio);
 void lock_page_memcg(struct page *page);
 void unlock_page_memcg(struct page *page);
 
@@ -1397,6 +1399,14 @@ static inline void unlock_page_memcg(struct page *page)
 {
 }
 
+static inline void folio_memcg_lock(struct folio *folio)
+{
+}
+
+static inline void folio_memcg_unlock(struct folio *folio)
+{
+}
+
 static inline void mem_cgroup_handle_over_high(void)
 {
 }

mm/memcontrol.c

@@ -1933,18 +1933,17 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
 }
 
 /**
- * lock_page_memcg - lock a page and memcg binding
- * @page: the page
+ * folio_memcg_lock - Bind a folio to its memcg.
+ * @folio: The folio.
  *
- * This function protects unlocked LRU pages from being moved to
+ * This function prevents unlocked LRU folios from being moved to
  * another cgroup.
  *
- * It ensures lifetime of the locked memcg. Caller is responsible
- * for the lifetime of the page.
+ * It ensures lifetime of the bound memcg.  The caller is responsible
+ * for the lifetime of the folio.
  */
-void lock_page_memcg(struct page *page)
+void folio_memcg_lock(struct folio *folio)
 {
-	struct page *head = compound_head(page); /* rmap on tail pages */
 	struct mem_cgroup *memcg;
 	unsigned long flags;
 
@@ -1958,7 +1957,7 @@ void lock_page_memcg(struct page *page)
 	if (mem_cgroup_disabled())
 		return;
 again:
-	memcg = page_memcg(head);
+	memcg = folio_memcg(folio);
 	if (unlikely(!memcg))
 		return;
 
@@ -1972,7 +1971,7 @@ again:
 		return;
 
 	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;
 	}
@@ -1986,9 +1985,15 @@ again:
 	memcg->move_lock_task = current;
 	memcg->move_lock_flags = flags;
 }
+EXPORT_SYMBOL(folio_memcg_lock);
+
+void lock_page_memcg(struct page *page)
+{
+	folio_memcg_lock(page_folio(page));
+}
 EXPORT_SYMBOL(lock_page_memcg);
 
-static void __unlock_page_memcg(struct mem_cgroup *memcg)
+static void __folio_memcg_unlock(struct mem_cgroup *memcg)
 {
 	if (memcg && memcg->move_lock_task == current) {
 		unsigned long flags = memcg->move_lock_flags;
@@ -2003,14 +2008,22 @@ static void __unlock_page_memcg(struct mem_cgroup *memcg)
 }
 
 /**
- * unlock_page_memcg - unlock a page and memcg binding
- * @page: the page
+ * folio_memcg_unlock - Release the binding between a folio and its memcg.
+ * @folio: The folio.
+ *
+ * This releases the binding created by folio_memcg_lock().  This does
+ * not change the accounting of this folio to its memcg, but it does
+ * permit others to change it.
  */
+void folio_memcg_unlock(struct folio *folio)
+{
+	__folio_memcg_unlock(folio_memcg(folio));
+}
+EXPORT_SYMBOL(folio_memcg_unlock);
+
 void unlock_page_memcg(struct page *page)
 {
-	struct page *head = compound_head(page);
-
-	__unlock_page_memcg(page_memcg(head));
+	folio_memcg_unlock(page_folio(page));
 }
 EXPORT_SYMBOL(unlock_page_memcg);
 
@@ -5643,7 +5656,7 @@ static int mem_cgroup_move_account(struct page *page,
 
 	page->memcg_data = (unsigned long)to;
 
-	__unlock_page_memcg(from);
+	__folio_memcg_unlock(from);
 
 	ret = 0;
 	nid = page_to_nid(page);