vmscan: convert lazy freeing to folios

Remove a hidden call to compound_head(), and account nr_pages instead of a
single page.  This matches the code in lru_lazyfree_fn() that accounts
nr_pages to PGLAZYFREE.

Link: https://lkml.kernel.org/r/20220504182857.4013401-12-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -1057,6 +1057,15 @@ static inline void count_memcg_page_event(struct page *page,
 		count_memcg_events(memcg, idx, 1);
 }
 
+static inline void count_memcg_folio_events(struct folio *folio,
+		enum vm_event_item idx, unsigned long nr)
+{
+	struct mem_cgroup *memcg = folio_memcg(folio);
+
+	if (memcg)
+		count_memcg_events(memcg, idx, nr);
+}
+
 static inline void count_memcg_event_mm(struct mm_struct *mm,
 					enum vm_event_item idx)
 {
@@ -1494,6 +1503,11 @@ static inline void count_memcg_page_event(struct page *page,
 {
 }
 
+static inline void count_memcg_folio_events(struct folio *folio,
+		enum vm_event_item idx, unsigned long nr)
+{
+}
+
 static inline
 void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx)
 {

mm/vmscan.c

@@ -1902,20 +1902,20 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 			}
 		}
 
-		if (PageAnon(page) && !PageSwapBacked(page)) {
+		if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) {
 			/* follow __remove_mapping for reference */
-			if (!page_ref_freeze(page, 1))
+			if (!folio_ref_freeze(folio, 1))
 				goto keep_locked;
 			/*
-			 * The page has only one reference left, which is
+			 * The folio has only one reference left, which is
 			 * from the isolation. After the caller puts the
-			 * page back on lru and drops the reference, the
-			 * page will be freed anyway. It doesn't matter
-			 * which lru it goes. So we don't bother checking
-			 * PageDirty here.
+			 * folio back on the lru and drops the reference, the
+			 * folio will be freed anyway. It doesn't matter
+			 * which lru it goes on. So we don't bother checking
+			 * the dirty flag here.
 			 */
-			count_vm_event(PGLAZYFREED);
-			count_memcg_page_event(page, PGLAZYFREED);
+			count_vm_events(PGLAZYFREED, nr_pages);
+			count_memcg_folio_events(folio, PGLAZYFREED, nr_pages);
 		} else if (!mapping || !__remove_mapping(mapping, folio, true,
 							 sc->target_mem_cgroup))
 			goto keep_locked;