[PATCH v3] mm/damon/ops-common: putback folios on invalid migrate nid

From: liyouhong <[email protected]>

damon_pa_migrate() and damos_va_migrate() isolate folios into a local list
and then call damon_migrate_pages().  When target_nid is invalid (including
the scheme default NUMA_NO_NODE / -1), damon_migrate_pages() returns early
without putting the folios back to the LRU.

Callers then discard the list head while those folios remain isolated with
an extra reference taken by folio_isolate_lru().  The pages stay off the
LRU for as long as the mapping exists (anon active+inactive counts drop
while RSS does not), and the leftover references can pin the pages after
the mapping is gone.

Put the folios back on the invalid-nid path so ignored migration requests
still return them to the LRU.

Fixes: 7e6c3130690a ("mm/damon/ops-common: ignore migration request to invalid nodes")
Cc: <[email protected]>
Assisted-by: Cursor:grok-4.5
Reviewed-by: SJ Park <[email protected]>
Signed-off-by: liyouhong <[email protected]>

---
v3:
- Drop the 2/2 cleanup patch as suggested; keep open-coded putback only

v2:
- Drop the putback helper for easier stable backport
- Open-code putback only on the invalid-nid path
- Keep the original indentation and Cc stable@
- Add a separate cleanup as 2/2 (factor out damon_putback_folio_list)

---
 mm/damon/ops-common.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index d1842e2b00ef..f5ded45fabd1 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -394,8 +394,15 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
 		return nr_migrated;
 
 	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
-			!node_state(target_nid, N_MEMORY))
+			!node_state(target_nid, N_MEMORY)) {
+		while (!list_empty(folio_list)) {
+			struct folio *folio = lru_to_folio(folio_list);
+
+			list_del(&folio->lru);
+			folio_putback_lru(folio);
+		}
 		return nr_migrated;
+	}
 
 	noreclaim_flag = memalloc_noreclaim_save();
 
-- 
2.25.1