mm: remove page_ref_sub_return()

With all callers converted to folios, we can act directly on
folio->_refcount.

Link: https://lkml.kernel.org/r/20240424191914.361554-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/page_ref.h

@@ -139,20 +139,15 @@ static inline void folio_ref_sub(struct folio *folio, int nr)
 	page_ref_sub(&folio->page, nr);
 }
 
-static inline int page_ref_sub_return(struct page *page, int nr)
+static inline int folio_ref_sub_return(struct folio *folio, int nr)
 {
-	int ret = atomic_sub_return(nr, &page->_refcount);
+	int ret = atomic_sub_return(nr, &folio->_refcount);
 
 	if (page_ref_tracepoint_active(page_ref_mod_and_return))
-		__page_ref_mod_and_return(page, -nr, ret);
+		__page_ref_mod_and_return(&folio->page, -nr, ret);
 	return ret;
 }
 
-static inline int folio_ref_sub_return(struct folio *folio, int nr)
-{
-	return page_ref_sub_return(&folio->page, nr);
-}
-
 static inline void page_ref_inc(struct page *page)
 {
 	atomic_inc(&page->_refcount);