mm: migrate: fix return value if all subpages of THPs are migrated successfully

During THP migration, if THPs are not migrated but they are split and all
subpages are migrated successfully, migrate_pages() will still return the
number of THP pages that were not migrated.  This will confuse the callers
of migrate_pages().  For example, the longterm pinning will failed though
all pages are migrated successfully.

Thus we should return 0 to indicate that all pages are migrated in this
case

Link: https://lkml.kernel.org/r/de386aa864be9158d2f3b344091419ea7c38b2f7.1666599848.git.baolin.wang@linux.alibaba.com
Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 1379e19..dff3335 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1582,6 +1582,13 @@ out:
         */
        list_splice(&ret_pages, from);
 
+       /*
+        * Return 0 in case all subpages of fail-to-migrate THPs are
+        * migrated successfully.
+        */
+       if (list_empty(from))
+               rc = 0;
+
        count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
        count_vm_events(PGMIGRATE_FAIL, nr_failed_pages);
        count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);