[PATCH 6/7] migrate_pages(): fix failure counting for THP splitting

[Huang Ying]

If THP is failed to be migrated, it may be split and retry.  But after
splitting, the head page will be left in "from" list, although THP
migration failure has been counted already.  If the head page is
failed to be migrated too, the failure will be counted twice
incorrectly.  So this is fixed in this patch via moving the head page
of THP after splitting to "thp_split_pages" too.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
---
 mm/migrate.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 9d1883d5927f..70a0e1f34c03 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1305,6 +1305,8 @@ static inline int try_split_thp(struct page *page, struct list_head *split_pages
 	lock_page(page);
 	rc = split_huge_page_to_list(page, split_pages);
 	unlock_page(page);
+	if (!rc)
+		list_move_tail(&page->lru, split_pages);
 
 	return rc;
 }
@@ -1364,7 +1366,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 		thp_retry = 0;
 
 		list_for_each_entry_safe(page, page2, from, lru) {
-retry:
 			/*
 			 * THP statistics is based on the source huge page.
 			 * Capture required information that might get lost
@@ -1411,7 +1412,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 					nr_thp_failed++;
 					if (!try_split_thp(page, &thp_split_pages)) {
 						nr_thp_split++;
-						goto retry;
+						break;
 					}
 				/* Hugetlb migration is unsupported */
 				} else if (!no_subpage_counting) {
@@ -1431,7 +1432,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 					/* THP NUMA faulting doesn't split THP to retry. */
 					if (!nosplit && !try_split_thp(page, &thp_split_pages)) {
 						nr_thp_split++;
-						goto retry;
+						break;
 					}
 				} else if (!no_subpage_counting) {
 					nr_failed++;
-- 
2.30.2