mm/ksm: use folio in stable_node_dup

Use ksm_get_folio() and save 2 compound_head calls.

Link: https://lkml.kernel.org/r/20240411061713.1847574-6-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

@@ -1638,7 +1638,7 @@ static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
 {
 	struct ksm_stable_node *dup, *found = NULL, *stable_node = *_stable_node;
 	struct hlist_node *hlist_safe;
-	struct page *_tree_page, *tree_page = NULL;
+	struct folio *folio, *tree_folio = NULL;
 	int nr = 0;
 	int found_rmap_hlist_len;
 
@@ -1657,24 +1657,24 @@ static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
 		 * We must walk all stable_node_dup to prune the stale
 		 * stable nodes during lookup.
 		 *
-		 * get_ksm_page can drop the nodes from the
+		 * ksm_get_folio can drop the nodes from the
 		 * stable_node->hlist if they point to freed pages
 		 * (that's why we do a _safe walk). The "dup"
 		 * stable_node parameter itself will be freed from
 		 * under us if it returns NULL.
 		 */
-		_tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
-		if (!_tree_page)
+		folio = ksm_get_folio(dup, GET_KSM_PAGE_NOLOCK);
+		if (!folio)
 			continue;
 		nr += 1;
 		if (is_page_sharing_candidate(dup)) {
 			if (!found ||
 			    dup->rmap_hlist_len > found_rmap_hlist_len) {
 				if (found)
-					put_page(tree_page);
+					folio_put(tree_folio);
 				found = dup;
 				found_rmap_hlist_len = found->rmap_hlist_len;
-				tree_page = _tree_page;
+				tree_folio = folio;
 
 				/* skip put_page for found dup */
 				if (!prune_stale_stable_nodes)
@@ -1682,7 +1682,7 @@ static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
 				continue;
 			}
 		}
-		put_page(_tree_page);
+		folio_put(folio);
 	}
 
 	if (found) {
@@ -1747,7 +1747,7 @@ static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
 	}
 
 	*_stable_node_dup = found;
-	return tree_page;
+	return &tree_folio->page;
 }
 
 static struct ksm_stable_node *stable_node_dup_any(struct ksm_stable_node *stable_node,