[PATCH v2 1/2] mm/damon/ops-common: putback folios on invalid migrate nid

[PATCH v2 1/2] mm/damon/ops-common: putback folios on invalid migrate nid

[dayou5941]

From: liyouhong <liyouhong@kylinos.cn>

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: <stable@vger.kernel.org>
Assisted-by: Cursor:grok-4.5
Signed-off-by: liyouhong <liyouhong@kylinos.cn>

---
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

[PATCH v2 2/2] mm/damon/ops-common: factor out damon_putback_folio_list()

[dayou5941]

From: liyouhong <liyouhong@kylinos.cn>

The putback loop is duplicated in damon_migrate_folio_list() and on the
invalid-nid path of damon_migrate_pages().  Factor it into a small helper
for readability.  No functional change.

Signed-off-by: liyouhong <liyouhong@kylinos.cn>
---
 mm/damon/ops-common.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index f5ded45fabd1..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;
 }
@@ -395,12 +401,7 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
 
 	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
 			!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);
-		}
+		damon_putback_folio_list(folio_list);
 		return nr_migrated;
 	}
 
-- 
2.25.1

Re: [PATCH v2 2/2] mm/damon/ops-common: factor out damon_putback_folio_list()

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Removal of the `struct folio *folio;` local variable declaration causes a build failure.
--

--- Patch [2]: [PATCH v2 2/2] mm/damon/ops-common: factor out damon_putback_folio_list() ---
commit 44363c3cc00338e3c3445bc5730a2655a4c0fded
Author: liyouhong <liyouhong@kylinos.cn>
mm/damon/ops-common: factor out damon_putback_folio_list()

This patch factors out the duplicated folio putback loop from
damon_migrate_folio_list() and damon_migrate_pages() into a new helper
function, damon_putback_folio_list().

> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index 0981a5e3af172..4b99c31122d6d 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
[ ... ]
> @@ -330,12 +330,22 @@ static unsigned int __damon_migrate_folio_list(
[ ... ]
>  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;

[Severity: Low]
Does removing this declaration result in a build failure? The folio variable
appears to still be used in damon_migrate_folio_list() during the initial
loop over folio_list:

	while (!list_empty(folio_list)) {
		cond_resched();

		folio = lru_to_folio(folio_list);
		list_del(&folio->lru);
        ...

>  	LIST_HEAD(ret_folios);
>  	LIST_HEAD(migrate_folios);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260724060135.3014676-1-dayou5941@163.com?part=2