mm/migrate: correct thp migration stats

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.

Clean up thp handling code too when we are there.

Fixes: 1a5bae25e3cf ("mm/vmstat: add events for THP migration without split")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lkml.kernel.org/r/20200917210413.1462975-1-zi.yan@sent.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index aecb143..04a98bb 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1446,7 +1446,7 @@ retry:
                         * Capture required information that might get lost
                         * during migration.
                         */
-                       is_thp = PageTransHuge(page);
+                       is_thp = PageTransHuge(page) && !PageHuge(page);
                        nr_subpages = thp_nr_pages(page);
                        cond_resched();
 
@@ -1472,7 +1472,7 @@ retry:
                                 * 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);
@@ -1481,8 +1481,7 @@ retry:
                                                nr_thp_split++;
                                                goto retry;
                                        }
-                               }
-                               if (is_thp) {
+
                                        nr_thp_failed++;
                                        nr_failed += nr_subpages;
                                        goto out;