migrate_pages(): fix THP failure counting for -ENOMEM

In unmap_and_move(), if the new THP cannot be allocated, -ENOMEM will be
returned, and migrate_pages() will try to split the THP unless "reason" is
MR_NUMA_MISPLACED (that is, nosplit == true).  But when nosplit == true,
the THP migration failure will not be counted.

This is incorrect, so in this patch, the THP migration failure will be
counted for -ENOMEM regardless of nosplit is true or false.  The nr_failed
counting isn't fixed because it's not used.  Added some comments for it
per Baolin's suggestion.

Link: https://lkml.kernel.org/r/20220817081408.513338-4-ying.huang@intel.com
Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
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>

diff --git a/mm/migrate.c b/mm/migrate.c
index 19a9b26af7e2c71d0a1f568b2eb3d8bb0423d817..ae55f08e72cecb956ae74dff1da6a04f5106943b 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1494,11 +1494,11 @@ retry:
                                /*
                                 * When memory is low, don't bother to try to migrate
                                 * other pages, just exit.
-                                * THP NUMA faulting doesn't split THP to retry.
                                 */
-                               if (is_thp && !nosplit) {
+                               if (is_thp) {
                                        nr_thp_failed++;
-                                       if (!try_split_thp(page, &thp_split_pages)) {
+                                       /* THP NUMA faulting doesn't split THP to retry. */
+                                       if (!nosplit && !try_split_thp(page, &thp_split_pages)) {
                                                nr_thp_split++;
                                                goto retry;
                                        }
@@ -1514,6 +1514,7 @@ retry:
                                 * the caller otherwise the page refcnt will be leaked.
                                 */
                                list_splice_init(&thp_split_pages, from);
+                               /* nr_failed isn't updated for not used */
                                nr_thp_failed += thp_retry;
                                goto out;
                        case -EAGAIN: