mm/migrate: putback split folios when numa hint migration fails

This issue is not from any report yet, but by code observation only.

This is yet another fix besides Hugh's patch [1] but on relevant code
path, where eager split of folio can happen if the folio is already on
deferred list during a folio migration.

Here the issue is NUMA path (migrate_misplaced_folio()) may start to
encounter such folio split now even with MR_NUMA_MISPLACED hint applied.
Then when migrate_pages() didn't migrate all the folios, it's possible the
split small folios be put onto the list instead of the original folio.
Then putting back only the head page won't be enough.

Fix it by putting back all the folios on the list.

[1] https://lore.kernel.org/all/46c948b4-4dd8-6e03-4c7b-ce4e81cfa536@google.com/

[akpm@linux-foundation.org: remove now unused local `nr_pages']
Link: https://lkml.kernel.org/r/20240708215537.2630610-1-peterx@redhat.com
Fixes: 7262f208ca68 ("mm/migrate: split source folio if it is on deferred split list")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: David Hildenbrand <david@redhat.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 6eb9df239230c2e6932aa0eb2e1278d923fa4be9..bdbb5bb04c91f4b8982341a96befb5b2ec86320f 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2621,20 +2621,13 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
        int nr_remaining;
        unsigned int nr_succeeded;
        LIST_HEAD(migratepages);
-       int nr_pages = folio_nr_pages(folio);
 
        list_add(&folio->lru, &migratepages);
        nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_folio,
                                     NULL, node, MIGRATE_ASYNC,
                                     MR_NUMA_MISPLACED, &nr_succeeded);
-       if (nr_remaining) {
-               if (!list_empty(&migratepages)) {
-                       list_del(&folio->lru);
-                       node_stat_mod_folio(folio, NR_ISOLATED_ANON +
-                                       folio_is_file_lru(folio), -nr_pages);
-                       folio_putback_lru(folio);
-               }
-       }
+       if (nr_remaining && !list_empty(&migratepages))
+               putback_movable_pages(&migratepages);
        if (nr_succeeded) {
                count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
                if (!node_is_toptier(folio_nid(folio)) && node_is_toptier(node))