[PATCH v2 2/4] mm: thp: introduce folio_split_queue_lock and its variants

Qi Zheng
2025-09-23T09:17:04Z

From: Muchun Song <songmuchun@bytedance.com>

In future memcg removal, the binding between a folio and a memcg may
change, making the split lock within the memcg unstable when held.

A new approach is required to reparent the split queue to its parent. This
patch starts introducing a unified way to acquire the split lock for
future work.

It's a code-only refactoring with no functional changes.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
---
include/linux/memcontrol.h | 10 ++++
mm/huge_memory.c | 104 ++++++++++++++++++++++++++++---------
2 files changed, 89 insertions(+), 25 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 16fe0306e50ea..99876af13c315 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1662,6 +1662,11 @@ int alloc_shrinker_info(struct mem_cgroup *memcg);
void free_shrinker_info(struct mem_cgroup *memcg);
void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
void reparent_shrinker_deferred(struct mem_cgroup *memcg);
+
+static inline int shrinker_id(struct shrinker *shrinker)
+{
+ return shrinker->id;
+}
#else
#define mem_cgroup_sockets_enabled 0

@@ -1693,6 +1698,11 @@ static inline void set_shrinker_bit(struct mem_cgroup *memcg,
int nid, int shrinker_id)
{
}
+
+static inline int shrinker_id(struct shrinker *shrinker)
+{
+ return -1;
+}
#endif

#ifdef CONFIG_MEMCG
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 582628ddf3f33..2f41b8f0d4871 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1078,26 +1078,83 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)

#ifdef CONFIG_MEMCG
static inline
-struct deferred_split *get_deferred_split_queue(struct folio *folio)
+struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
+ struct deferred_split *queue)
{
- struct mem_cgroup *memcg = folio_memcg(folio);
- struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
+ if (mem_cgroup_disabled())
+ return NULL;
+ if (&NODE_DATA(folio_nid(folio))->deferred_split_queue == queue)
+ return NULL;
+ return container_of(queue, struct mem_cgroup, deferred_split_queue);
+}

- if (memcg)
- return &memcg->deferred_split_queue;
- else
- return &pgdat->deferred_split_queue;
+static struct deferred_split *folio_split_queue_lock(struct folio *folio)
+{
+ struct mem_cgroup *memcg;
+ struct deferred_split *queue;
+
+ memcg = folio_memcg(folio);
+ queue = memcg ? &memcg->deferred_split_queue :
+ &NODE_DATA(folio_nid(folio))->deferred_split_queue;
+ spin_lock(&queue->split_queue_lock);
+
+ return queue;
+}
+
+static struct deferred_split *
+folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
+{
+ struct mem_cgroup *memcg;
+ struct deferred_split *queue;
+
+ memcg = folio_memcg(folio);
+ queue = memcg ? &memcg->deferred_split_queue :
+ &NODE_DATA(folio_nid(folio))->deferred_split_queue;
+ spin_lock_irqsave(&queue->split_queue_lock, *flags);
+
+ return queue;
}
#else
static inline
-struct deferred_split *get_deferred_split_queue(struct folio *folio)
+struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
+ struct deferred_split *queue)
+{
+ return NULL;
+}
+
+static struct deferred_split *folio_split_queue_lock(struct folio *folio)
{
struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
+ struct deferred_split *queue = &pgdat->deferred_split_queue;
+
+ spin_lock(&queue->split_queue_lock);

- return &pgdat->deferred_split_queue;
+ return queue;
+}
+
+static struct deferred_split *
+folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
+{
+ struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
+ struct deferred_split *queue = &pgdat->deferred_split_queue;
+
+ spin_lock_irqsave(&queue->split_queue_lock, *flags);
+
+ return queue;
}
#endif

+static inline void split_queue_unlock(struct deferred_split *queue)
+{
+ spin_unlock(&queue->split_queue_lock);
+}
+
+static inline void split_queue_unlock_irqrestore(struct deferred_split *queue,
+ unsigned long flags)
+{
+ spin_unlock_irqrestore(&queue->split_queue_lock, flags);
+}
+
static inline bool is_transparent_hugepage(const struct folio *folio)
{
if (!folio_test_large(folio))
@@ -3579,7 +3636,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
struct page *split_at, struct page *lock_at,
struct list_head *list, bool uniform_split)
{
- struct deferred_split *ds_queue = get_deferred_split_queue(folio);
+ struct deferred_split *ds_queue;
XA_STATE(xas, &folio->mapping->i_pages, folio->index);
struct folio *end_folio = folio_next(folio);
bool is_anon = folio_test_anon(folio);
@@ -3718,7 +3775,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
}

/* Prevent deferred_split_scan() touching ->_refcount */
- spin_lock(&ds_queue->split_queue_lock);
+ ds_queue = folio_split_queue_lock(folio);
if (folio_ref_freeze(folio, 1 + extra_pins)) {
struct swap_cluster_info *ci = NULL;
struct lruvec *lruvec;
@@ -3740,7 +3797,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
*/
list_del_init(&folio->_deferred_list);
}
- spin_unlock(&ds_queue->split_queue_lock);
+ split_queue_unlock(ds_queue);
if (mapping) {
int nr = folio_nr_pages(folio);

@@ -3835,7 +3892,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
if (ci)
swap_cluster_unlock(ci);
} else {
- spin_unlock(&ds_queue->split_queue_lock);
+ split_queue_unlock(ds_queue);
ret = -EAGAIN;
}
fail:
@@ -4016,8 +4073,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
WARN_ON_ONCE(folio_ref_count(folio));
WARN_ON_ONCE(!mem_cgroup_disabled() && !folio_memcg_charged(folio));

- ds_queue = get_deferred_split_queue(folio);
- spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+ ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
if (!list_empty(&folio->_deferred_list)) {
ds_queue->split_queue_len--;
if (folio_test_partially_mapped(folio)) {
@@ -4028,7 +4084,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
list_del_init(&folio->_deferred_list);
unqueued = true;
}
- spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
+ split_queue_unlock_irqrestore(ds_queue, flags);

return unqueued; /* useful for debug warnings */
}
@@ -4036,10 +4092,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
/* partially_mapped=false won't clear PG_partially_mapped folio flag */
void deferred_split_folio(struct folio *folio, bool partially_mapped)
{
- struct deferred_split *ds_queue = get_deferred_split_queue(folio);
-#ifdef CONFIG_MEMCG
- struct mem_cgroup *memcg = folio_memcg(folio);
-#endif
+ struct deferred_split *ds_queue;
unsigned long flags;

/*
@@ -4062,7 +4115,7 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
if (folio_test_swapcache(folio))
return;

- spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+ ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
if (partially_mapped) {
if (!folio_test_partially_mapped(folio)) {
folio_set_partially_mapped(folio);
@@ -4077,15 +4130,16 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
VM_WARN_ON_FOLIO(folio_test_partially_mapped(folio), folio);
}
if (list_empty(&folio->_deferred_list)) {
+ struct mem_cgroup *memcg;
+
+ memcg = folio_split_queue_memcg(folio, ds_queue);
list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
ds_queue->split_queue_len++;
-#ifdef CONFIG_MEMCG
if (memcg)
set_shrinker_bit(memcg, folio_nid(folio),
- deferred_split_shrinker->id);
-#endif
+ shrinker_id(deferred_split_shrinker));
}
- spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
+ split_queue_unlock_irqrestore(ds_queue, flags);
}

static unsigned long deferred_split_count(struct shrinker *shrink,
--
2.20.1