Re: [PATCH] mm/migrate: correct thp migration stats.

[Daniel Jordan <daniel.m.jordan@oracle.com>]

On Thu, Sep 17, 2020 at 04:27:29PM -0400, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> PageTransHuge returns true for both thp and hugetlb, so thp stats was
> counting both thp and hugetlb migrations. Exclude hugetlb migration by
> setting is_thp variable right.

Yeah, shoot.

> Fixes: 1a5bae25e3cf ("mm/vmstat: add events for THP migration without split")
> Signed-off-by: Zi Yan <ziy@nvidia.com>

Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>

If you wanted, you could also do this.

diff --git a/mm/migrate.c b/mm/migrate.c
index d1ad964165e5..6bc9559afc70 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1471,7 +1471,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				 * we encounter them after the rest of the list
 				 * is processed.
 				 */
-				if (PageTransHuge(page) && !PageHuge(page)) {
+				if (is_thp) {
 					lock_page(page);
 					rc = split_huge_page_to_list(page, from);
 					unlock_page(page);
@@ -1480,8 +1480,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 						nr_thp_split++;
 						goto retry;
 					}
-				}
-				if (is_thp) {
+
 					nr_thp_failed++;
 					nr_failed += nr_subpages;
 					goto out;