migrate_pages(): remove unnecessary list_safe_reset_next()

Before commit b5bade9 ("mm: migrate: fix the return value of
migrate_pages()"), the tail pages of THP will be put in the "from"
list directly.  So one of the loop cursors (page2) needs to be reset,
as is done in try_split_thp() via list_safe_reset_next().  But after
the commit, the tail pages of THP will be put in a dedicated
list (thp_split_pages).  That is, the "from" list will not be changed
during splitting.  So, it's unnecessary to call list_safe_reset_next()
anymore.

This is a code cleanup, no functionality changes are expected.

Link: https://lkml.kernel.org/r/20220817081408.513338-3-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/migrate.c

@@ -1369,16 +1369,13 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	return rc;
 }
 
-static inline int try_split_thp(struct page *page, struct page **page2,
-				struct list_head *from)
+static inline int try_split_thp(struct page *page, struct list_head *split_pages)
 {
-	int rc = 0;
+	int rc;
 
 	lock_page(page);
-	rc = split_huge_page_to_list(page, from);
+	rc = split_huge_page_to_list(page, split_pages);
 	unlock_page(page);
-	if (!rc)
-		list_safe_reset_next(page, *page2, lru);
 
 	return rc;
 }
@@ -1482,7 +1479,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				/* THP migration is unsupported */
 				if (is_thp) {
 					nr_thp_failed++;
-					if (!try_split_thp(page, &page2, &thp_split_pages)) {
+					if (!try_split_thp(page, &thp_split_pages)) {
 						nr_thp_split++;
 						goto retry;
 					}
@@ -1501,7 +1498,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				 */
 				if (is_thp && !nosplit) {
 					nr_thp_failed++;
-					if (!try_split_thp(page, &page2, &thp_split_pages)) {
+					if (!try_split_thp(page, &thp_split_pages)) {
 						nr_thp_split++;
 						goto retry;
 					}