[PATCH v1 12/26] mm: migrate: prevent memory cgroup release in folio_migrate_mapping()

Qi Zheng
2025-10-28T14:03:36Z

From: Muchun Song <songmuchun@bytedance.com>

In the near future, a folio will no longer pin its corresponding
memory cgroup. To ensure safety, it will only be appropriate to
hold the rcu read lock or acquire a reference to the memory cgroup
returned by folio_memcg(), thereby preventing it from being released.

In the current patch, the rcu read lock is employed to safeguard
against the release of the memory cgroup in folio_migrate_mapping().

This serves as a preparatory measure for the reparenting of the
LRU pages.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
mm/migrate.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index ceee354ef2152..cdab1b652c530 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -664,6 +664,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
struct lruvec *old_lruvec, *new_lruvec;
struct mem_cgroup *memcg;

+ rcu_read_lock();
memcg = folio_memcg(folio);
old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat);
new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat);
@@ -691,6 +692,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
__mod_lruvec_state(new_lruvec, NR_FILE_DIRTY, nr);
__mod_zone_page_state(newzone, NR_ZONE_WRITE_PENDING, nr);
}
+ rcu_read_unlock();
}
local_irq_enable();

--
2.20.1