mm/ksm: use folio in remove_stable_node

Pages in stable tree are all single normal page, so uses ksm_get_folio()
and folio_set_stable_node(), also saves 3 calls to compound_head().

Link: https://lkml.kernel.org/r/20240411061713.1847574-5-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

@@ -1121,13 +1121,13 @@ static inline void folio_set_stable_node(struct folio *folio,
  */
 static int remove_stable_node(struct ksm_stable_node *stable_node)
 {
-	struct page *page;
+	struct folio *folio;
 	int err;
 
-	page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
-	if (!page) {
+	folio = ksm_get_folio(stable_node, GET_KSM_PAGE_LOCK);
+	if (!folio) {
 		/*
-		 * get_ksm_page did remove_node_from_stable_tree itself.
+		 * ksm_get_folio did remove_node_from_stable_tree itself.
 		 */
 		return 0;
 	}
@@ -1138,22 +1138,22 @@ static int remove_stable_node(struct ksm_stable_node *stable_node)
 	 * merge_across_nodes/max_page_sharing be switched.
 	 */
 	err = -EBUSY;
-	if (!page_mapped(page)) {
+	if (!folio_mapped(folio)) {
 		/*
-		 * The stable node did not yet appear stale to get_ksm_page(),
-		 * since that allows for an unmapped ksm page to be recognized
+		 * The stable node did not yet appear stale to ksm_get_folio(),
+		 * since that allows for an unmapped ksm folio to be recognized
 		 * right up until it is freed; but the node is safe to remove.
-		 * This page might be in an LRU cache waiting to be freed,
-		 * or it might be PageSwapCache (perhaps under writeback),
+		 * This folio might be in an LRU cache waiting to be freed,
+		 * or it might be in the swapcache (perhaps under writeback),
 		 * or it might have been removed from swapcache a moment ago.
 		 */
-		set_page_stable_node(page, NULL);
+		folio_set_stable_node(folio, NULL);
 		remove_node_from_stable_tree(stable_node);
 		err = 0;
 	}
 
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 	return err;
 }