mm: migrate: convert migrate_misplaced_page() to migrate_misplaced_folio()

At present, numa balance only support base page and PMD-mapped THP, but we
will expand to support to migrate large folio/pte-mapped THP in the
future, it is better to make migrate_misplaced_page() to take a folio
instead of a page, and rename it to migrate_misplaced_folio(), it is a
preparation, also this remove several compound_head() calls.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Kefeng Wang <[e-mail]>
Reviewed-by: Zi Yan <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: "Huang, Ying" <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/migrate.h

···
 }
 
 #ifdef CONFIG_NUMA_BALANCING
-int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
+int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
 			   int node);
 #else
-static inline int migrate_misplaced_page(struct page *page,
+static inline int migrate_misplaced_folio(struct folio *folio,
 					 struct vm_area_struct *vma, int node)
 {
 	return -EAGAIN; /* can't migrate now */

mm/huge_memory.c

···
 	spin_unlock(vmf->ptl);
 	writable = false;
 
-	migrated = migrate_misplaced_page(page, vma, target_nid);
+	migrated = migrate_misplaced_folio(page_folio(page), vma, target_nid);
 	if (migrated) {
 		flags |= TNF_MIGRATED;
 		page_nid = target_nid;

mm/memory.c

···
 	writable = false;
 
 	/* Migrate to the requested node */
-	if (migrate_misplaced_page(page, vma, target_nid)) {
+	if (migrate_misplaced_folio(page_folio(page), vma, target_nid)) {
 		page_nid = target_nid;
 		flags |= TNF_MIGRATED;
 	} else {

mm/migrate.c

···
 }
 
 /*
- * Attempt to migrate a misplaced page to the specified destination
+ * Attempt to migrate a misplaced folio to the specified destination
  * node. Caller is expected to have an elevated reference count on
- * the page that will be dropped by this function before returning.
+ * the folio that will be dropped by this function before returning.
  */
-int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
-			   int node)
+int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
+			    int node)
 {
 	pg_data_t *pgdat = NODE_DATA(node);
 	int isolated;
 	int nr_remaining;
 	unsigned int nr_succeeded;
 	LIST_HEAD(migratepages);
-	int nr_pages = thp_nr_pages(page);
+	int nr_pages = folio_nr_pages(folio);
 
 	/*
-	 * Don't migrate file pages that are mapped in multiple processes
+	 * Don't migrate file folios that are mapped in multiple processes
 	 * with execute permissions as they are probably shared libraries.
+	 * To check if the folio is shared, ideally we want to make sure
+	 * every page is mapped to the same process. Doing that is very
+	 * expensive, so check the estimated mapcount of the folio instead.
 	 */
-	if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
+	if (folio_estimated_sharers(folio) != 1 && folio_is_file_lru(folio) &&
 	    (vma->vm_flags & VM_EXEC))
 		goto out;
 
 	/*
-	 * Also do not migrate dirty pages as not all filesystems can move
-	 * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles.
+	 * Also do not migrate dirty folios as not all filesystems can move
+	 * dirty folios in MIGRATE_ASYNC mode which is a waste of cycles.
 	 */
-	if (page_is_file_lru(page) && PageDirty(page))
+	if (folio_is_file_lru(folio) && folio_test_dirty(folio))
 		goto out;
 
-	isolated = numamigrate_isolate_folio(pgdat, page_folio(page));
+	isolated = numamigrate_isolate_folio(pgdat, folio);
 	if (!isolated)
 		goto out;
 
-	list_add(&page->lru, &migratepages);
+	list_add(&folio->lru, &migratepages);
 	nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_folio,
 				     NULL, node, MIGRATE_ASYNC,
 				     MR_NUMA_MISPLACED, &nr_succeeded);
 	if (nr_remaining) {
 		if (!list_empty(&migratepages)) {
-			list_del(&page->lru);
-			mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
-					page_is_file_lru(page), -nr_pages);
-			putback_lru_page(page);
+			list_del(&folio->lru);
+			node_stat_mod_folio(folio, NR_ISOLATED_ANON +
+					folio_is_file_lru(folio), -nr_pages);
+			folio_putback_lru(folio);
 		}
 		isolated = 0;
 	}
 	if (nr_succeeded) {
 		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
-		if (!node_is_toptier(page_to_nid(page)) && node_is_toptier(node))
+		if (!node_is_toptier(folio_nid(folio)) && node_is_toptier(node))
 			mod_node_page_state(pgdat, PGPROMOTE_SUCCESS,
 					    nr_succeeded);
 	}
···
 	return isolated;
 
 out:
-	put_page(page);
+	folio_put(folio);
 	return 0;
 }
 #endif /* CONFIG_NUMA_BALANCING */