mm: migrate_device: convert try_to_migrate() to folios

JIRA: https://issues.redhat.com/browse/RHEL-84184
JIRA: https://issues.redhat.com/browse/RHEL-83249
Upstream Status: RHEL only

These are hunks from upstream's commit 4b8554c ("mm/rmap: Convert
try_to_migrate() to folios") that ended up lost in RHEL-9 due to
out-of-order backports of commits 4b8554c and 76cbbea
("mm: move the migrate_vma_* device migration code into its own file").

There is nothing functionally wrong with the current RHEL-9 backported
code, but it is better to bring these bits back to their original
upstream form, so it becomes easier and less error-prone to perform
further backports to this area in the future.

Signed-off-by: Rafael Aquini <raquini@redhat.com>

Author: Rafael Aquini

mm/migrate_device.c

@@ -366,6 +366,7 @@ static unsigned long migrate_device_unmap(unsigned long *src_pfns,
 
 	for (i = 0; i < npages; i++) {
 		struct page *page = migrate_pfn_to_page(src_pfns[i]);
+		struct folio *folio;
 
 		if (!page) {
 			if (src_pfns[i] & MIGRATE_PFN_MIGRATE)
@@ -391,8 +392,9 @@ static unsigned long migrate_device_unmap(unsigned long *src_pfns,
 			put_page(page);
 		}
 
-		if (page_mapped(page))
-			try_to_migrate(page_folio(page), 0);
+		folio = page_folio(page);
+		if (folio_mapped(folio))
+			try_to_migrate(folio, 0);
 
 		if (page_mapped(page) ||
 		    !migrate_vma_check_page(page, fault_page)) {