mm/ksm: add folio_set_stable_node

Turn set_page_stable_node() into a wrapper folio_set_stable_node, and then
use it to replace the former.  we will merge them together after all place
converted to folio.

Link: https://lkml.kernel.org/r/20240411061713.1847574-4-alexs@kernel.orgSigned-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/ksm.c

@@ -1109,6 +1109,12 @@ static inline void set_page_stable_node(struct page *page,
 	page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
 }
 
+static inline void folio_set_stable_node(struct folio *folio,
+					 struct ksm_stable_node *stable_node)
+{
+	set_page_stable_node(&folio->page, stable_node);
+}
+
 #ifdef CONFIG_SYSFS
 /*
  * Only called through the sysfs control interface:
@@ -3241,7 +3247,7 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio)
 		 * has gone stale (or that folio_test_swapcache has been cleared).
 		 */
 		smp_wmb();
-		set_page_stable_node(&folio->page, NULL);
+		folio_set_stable_node(folio, NULL);
 	}
 }
 #endif /* CONFIG_MIGRATION */