[PATCH] 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.

Factor the existing putback loop into damon_putback_folio_list() and use it
on the invalid-nid path as well, so ignored migration requests still return
folios to the LRU.

Fixes: 7e6c3130690a ("mm/damon/ops-common: ignore migration request to invalid nodes")
Signed-off-by: liyouhong <[email protected]>
---
 mm/damon/ops-common.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index d1842e2b00ef..9a1e8aec5444 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -331,12 +331,22 @@ static unsigned int __damon_migrate_folio_list(
 	return nr_succeeded;
 }
 
+static void damon_putback_folio_list(struct list_head *folio_list)
+{
+	struct folio *folio;
+
+	while (!list_empty(folio_list)) {
+		folio = lru_to_folio(folio_list);
+		list_del(&folio->lru);
+		folio_putback_lru(folio);
+	}
+}
+
 static unsigned int damon_migrate_folio_list(struct list_head *folio_list,
 						struct pglist_data *pgdat,
 						int target_nid)
 {
 	unsigned int nr_migrated = 0;
-	struct folio *folio;
 	LIST_HEAD(ret_folios);
 	LIST_HEAD(migrate_folios);
 
@@ -374,11 +384,7 @@ static unsigned int damon_migrate_folio_list(struct list_head *folio_list,
 
 	list_splice(&ret_folios, folio_list);
 
-	while (!list_empty(folio_list)) {
-		folio = lru_to_folio(folio_list);
-		list_del(&folio->lru);
-		folio_putback_lru(folio);
-	}
+	damon_putback_folio_list(folio_list);
 
 	return nr_migrated;
 }
@@ -394,8 +400,10 @@ 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)) {
+		damon_putback_folio_list(folio_list);
 		return nr_migrated;
+	}
 
 	noreclaim_flag = memalloc_noreclaim_save();