Three small folio patches.

One bug fix, one patch pulled forward from the patches destined for 5.18
 and then a patch to make use of that functionality.
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Merge tag 'folio-5.17a' of git://git.infradead.org/users/willy/pagecache

Pull more folio updates from Matthew Wilcox:
 "Three small folio patches.

  One bug fix, one patch pulled forward from the patches destined for
  5.18 and then a patch to make use of that functionality"

* tag 'folio-5.17a' of git://git.infradead.org/users/willy/pagecache:
  filemap: Use folio_put_refs() in filemap_free_folio()
  mm: Add folio_put_refs()
  pagevec: Initialise folio_batch->percpu_pvec_drained

include/linux/mm.h

@@ -1199,6 +1199,26 @@ static inline void folio_put(struct folio *folio)
 		__put_page(&folio->page);
 }
 
+/**
+ * folio_put_refs - Reduce the reference count on a folio.
+ * @folio: The folio.
+ * @refs: The amount to subtract from the folio's reference count.
+ *
+ * If the folio's reference count reaches zero, the memory will be
+ * released back to the page allocator and may be used by another
+ * allocation immediately.  Do not access the memory or the struct folio
+ * after calling folio_put_refs() unless you can be sure that these weren't
+ * the last references.
+ *
+ * Context: May be called in process or interrupt context, but not in NMI
+ * context.  May be called while holding a spinlock.
+ */
+static inline void folio_put_refs(struct folio *folio, int refs)
+{
+	if (folio_ref_sub_and_test(folio, refs))
+		__put_page(&folio->page);
+}
+
 static inline void put_page(struct page *page)
 {
 	struct folio *folio = page_folio(page);

include/linux/pagevec.h

@@ -111,6 +111,7 @@ static_assert(offsetof(struct pagevec, pages) ==
 static inline void folio_batch_init(struct folio_batch *fbatch)
 {
 	fbatch->nr = 0;
+	fbatch->percpu_pvec_drained = false;
 }
 
 static inline unsigned int folio_batch_count(struct folio_batch *fbatch)

mm/filemap.c

@@ -231,17 +231,15 @@ void __filemap_remove_folio(struct folio *folio, void *shadow)
 void filemap_free_folio(struct address_space *mapping, struct folio *folio)
 {
 	void (*freepage)(struct page *);
+	int refs = 1;
 
 	freepage = mapping->a_ops->freepage;
 	if (freepage)
 		freepage(&folio->page);
 
-	if (folio_test_large(folio) && !folio_test_hugetlb(folio)) {
-		folio_ref_sub(folio, folio_nr_pages(folio));
-		VM_BUG_ON_FOLIO(folio_ref_count(folio) <= 0, folio);
-	} else {
-		folio_put(folio);
-	}
+	if (folio_test_large(folio) && !folio_test_hugetlb(folio))
+		refs = folio_nr_pages(folio);
+	folio_put_refs(folio, refs);
 }
 
 /**