[PATCH] mm: switch deferred split shrinker to list_lru

[PATCH] mm: switch deferred split shrinker to list_lru

[Johannes Weiner]

The deferred split queue handles cgroups in a suboptimal fashion. The
queue is per-NUMA node or per-cgroup, not the intersection. That means
on a cgrouped system, a node-restricted allocation entering reclaim
can end up splitting large pages on other nodes:

	alloc/unmap
	  deferred_split_folio()
	    list_add_tail(memcg->split_queue)
	    set_shrinker_bit(memcg, node, deferred_shrinker_id)

	for_each_zone_zonelist_nodemask(restricted_nodes)
	  mem_cgroup_iter()
	    shrink_slab(node, memcg)
	      shrink_slab_memcg(node, memcg)
	        if test_shrinker_bit(memcg, node, deferred_shrinker_id)
	          deferred_split_scan()
	            walks memcg->split_queue

The shrinker bit adds an imperfect guard rail. As soon as the cgroup
has a single large page on the node of interest, all large pages owned
by that memcg, including those on other nodes, will be split.

list_lru properly sets up per-node, per-cgroup lists. As a bonus, it
streamlines a lot of the list operations and reclaim walks. It's used
widely by other major shrinkers already. Convert the deferred split
queue as well.

The list_lru per-memcg heads are instantiated on demand when the first
object of interest is allocated for a cgroup, by calling
memcg_list_lru_alloc(). Add calls to where splittable pages are
created: anon faults, swapin faults, khugepaged collapse.

These calls create all possible node heads for the cgroup at once, so
the migration code (between nodes) doesn't need any special care.

The folio_test_partially_mapped() state is currently protected and
serialized wrt LRU state by the deferred split queue lock. To
facilitate the transition, add helpers to the list_lru API to allow
caller-side locking.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/huge_mm.h    |   6 +-
 include/linux/list_lru.h   |  48 ++++++
 include/linux/memcontrol.h |   4 -
 include/linux/mmzone.h     |  12 --
 mm/huge_memory.c           | 326 +++++++++++--------------------------
 mm/internal.h              |   2 +-
 mm/khugepaged.c            |   7 +
 mm/list_lru.c              | 197 ++++++++++++++--------
 mm/memcontrol.c            |  12 +-
 mm/memory.c                |  52 +++---
 mm/mm_init.c               |  14 --
 11 files changed, 310 insertions(+), 370 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index a4d9f964dfde..2d0d0c797dd8 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -414,10 +414,9 @@ static inline int split_huge_page(struct page *page)
 {
 	return split_huge_page_to_list_to_order(page, NULL, 0);
 }
+
+extern struct list_lru deferred_split_lru;
 void deferred_split_folio(struct folio *folio, bool partially_mapped);
-#ifdef CONFIG_MEMCG
-void reparent_deferred_split_queue(struct mem_cgroup *memcg);
-#endif
 
 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 		unsigned long address, bool freeze);
@@ -650,7 +649,6 @@ static inline int try_folio_split_to_order(struct folio *folio,
 }
 
 static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
-static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {}
 #define split_huge_pmd(__vma, __pmd, __address)	\
 	do { } while (0)
 
diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index fe739d35a864..d75f25778ba1 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -81,8 +81,56 @@ static inline int list_lru_init_memcg_key(struct list_lru *lru, struct shrinker
 
 int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
 			 gfp_t gfp);
+
+#ifdef CONFIG_MEMCG
+int memcg_list_lru_alloc_folio(struct folio *folio, struct list_lru *lru,
+			       gfp_t gfp);
+#else
+static inline int memcg_list_lru_alloc_folio(struct folio *folio,
+					     struct list_lru *lru, gfp_t gfp)
+{
+	return 0;
+}
+#endif
+
 void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *parent);
 
+/**
+ * list_lru_lock: lock the sublist for the given node and memcg
+ * @lru: the lru pointer
+ * @nid: the node id of the sublist to lock.
+ * @memcg: the cgroup of the sublist to lock.
+ *
+ * Returns the locked list_lru_one sublist. The caller must call
+ * list_lru_unlock() when done.
+ *
+ * You must ensure that the memcg is not freed during this call (e.g., with
+ * rcu or by taking a css refcnt).
+ *
+ * Return: the locked list_lru_one, or NULL on failure
+ */
+struct list_lru_one *list_lru_lock(struct list_lru *lru, int nid,
+				   struct mem_cgroup *memcg);
+
+/**
+ * list_lru_unlock: unlock a sublist locked by list_lru_lock()
+ * @l: the list_lru_one to unlock
+ */
+void list_lru_unlock(struct list_lru_one *l);
+
+struct list_lru_one *list_lru_lock_irqsave(struct list_lru *lru, int nid,
+					   struct mem_cgroup *memcg,
+					   unsigned long *irq_flags);
+void list_lru_unlock_irqrestore(struct list_lru_one *l,
+				unsigned long *irq_flags);
+
+/* Caller-locked variants, see list_lru_add() etc for documentation */
+bool __list_lru_add(struct list_lru *lru, struct list_lru_one *l,
+		    struct list_head *item, int nid,
+		    struct mem_cgroup *memcg);
+bool __list_lru_del(struct list_lru *lru, struct list_lru_one *l,
+		    struct list_head *item, int nid);
+
 /**
  * list_lru_add: add an element to the lru list's tail
  * @lru: the lru pointer
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 086158969529..0782c72a1997 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -277,10 +277,6 @@ struct mem_cgroup {
 	struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT];
 #endif
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct deferred_split deferred_split_queue;
-#endif
-
 #ifdef CONFIG_LRU_GEN_WALKS_MMU
 	/* per-memcg mm_struct list */
 	struct lru_gen_mm_list mm_list;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 7bd0134c241c..232b7a71fd69 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1429,14 +1429,6 @@ struct zonelist {
  */
 extern struct page *mem_map;
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-struct deferred_split {
-	spinlock_t split_queue_lock;
-	struct list_head split_queue;
-	unsigned long split_queue_len;
-};
-#endif
-
 #ifdef CONFIG_MEMORY_FAILURE
 /*
  * Per NUMA node memory failure handling statistics.
@@ -1562,10 +1554,6 @@ typedef struct pglist_data {
 	unsigned long first_deferred_pfn;
 #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct deferred_split deferred_split_queue;
-#endif
-
 #ifdef CONFIG_NUMA_BALANCING
 	/* start time in ms of current promote rate limit period */
 	unsigned int nbp_rl_start;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7d0a64033b18..f43051eaf089 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -14,6 +14,7 @@
 #include <linux/mmu_notifier.h>
 #include <linux/rmap.h>
 #include <linux/swap.h>
+#include <linux/list_lru.h>
 #include <linux/shrinker.h>
 #include <linux/mm_inline.h>
 #include <linux/swapops.h>
@@ -67,6 +68,7 @@ unsigned long transparent_hugepage_flags __read_mostly =
 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 
+struct list_lru deferred_split_lru;
 static struct shrinker *deferred_split_shrinker;
 static unsigned long deferred_split_count(struct shrinker *shrink,
 					  struct shrink_control *sc);
@@ -866,6 +868,11 @@ static int __init thp_shrinker_init(void)
 	if (!deferred_split_shrinker)
 		return -ENOMEM;
 
+	if (list_lru_init_memcg(&deferred_split_lru, deferred_split_shrinker)) {
+		shrinker_free(deferred_split_shrinker);
+		return -ENOMEM;
+	}
+
 	deferred_split_shrinker->count_objects = deferred_split_count;
 	deferred_split_shrinker->scan_objects = deferred_split_scan;
 	shrinker_register(deferred_split_shrinker);
@@ -886,6 +893,7 @@ static int __init thp_shrinker_init(void)
 
 	huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero");
 	if (!huge_zero_folio_shrinker) {
+		list_lru_destroy(&deferred_split_lru);
 		shrinker_free(deferred_split_shrinker);
 		return -ENOMEM;
 	}
@@ -900,6 +908,7 @@ static int __init thp_shrinker_init(void)
 static void __init thp_shrinker_exit(void)
 {
 	shrinker_free(huge_zero_folio_shrinker);
+	list_lru_destroy(&deferred_split_lru);
 	shrinker_free(deferred_split_shrinker);
 }
 
@@ -1080,119 +1089,6 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 	return pmd;
 }
 
-static struct deferred_split *split_queue_node(int nid)
-{
-	struct pglist_data *pgdata = NODE_DATA(nid);
-
-	return &pgdata->deferred_split_queue;
-}
-
-#ifdef CONFIG_MEMCG
-static inline
-struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
-					   struct deferred_split *queue)
-{
-	if (mem_cgroup_disabled())
-		return NULL;
-	if (split_queue_node(folio_nid(folio)) == queue)
-		return NULL;
-	return container_of(queue, struct mem_cgroup, deferred_split_queue);
-}
-
-static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memcg)
-{
-	return memcg ? &memcg->deferred_split_queue : split_queue_node(nid);
-}
-#else
-static inline
-struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
-					   struct deferred_split *queue)
-{
-	return NULL;
-}
-
-static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memcg)
-{
-	return split_queue_node(nid);
-}
-#endif
-
-static struct deferred_split *split_queue_lock(int nid, struct mem_cgroup *memcg)
-{
-	struct deferred_split *queue;
-
-retry:
-	queue = memcg_split_queue(nid, memcg);
-	spin_lock(&queue->split_queue_lock);
-	/*
-	 * There is a period between setting memcg to dying and reparenting
-	 * deferred split queue, and during this period the THPs in the deferred
-	 * split queue will be hidden from the shrinker side.
-	 */
-	if (unlikely(memcg_is_dying(memcg))) {
-		spin_unlock(&queue->split_queue_lock);
-		memcg = parent_mem_cgroup(memcg);
-		goto retry;
-	}
-
-	return queue;
-}
-
-static struct deferred_split *
-split_queue_lock_irqsave(int nid, struct mem_cgroup *memcg, unsigned long *flags)
-{
-	struct deferred_split *queue;
-
-retry:
-	queue = memcg_split_queue(nid, memcg);
-	spin_lock_irqsave(&queue->split_queue_lock, *flags);
-	if (unlikely(memcg_is_dying(memcg))) {
-		spin_unlock_irqrestore(&queue->split_queue_lock, *flags);
-		memcg = parent_mem_cgroup(memcg);
-		goto retry;
-	}
-
-	return queue;
-}
-
-static struct deferred_split *folio_split_queue_lock(struct folio *folio)
-{
-	struct deferred_split *queue;
-
-	rcu_read_lock();
-	queue = split_queue_lock(folio_nid(folio), folio_memcg(folio));
-	/*
-	 * The memcg destruction path is acquiring the split queue lock for
-	 * reparenting. Once you have it locked, it's safe to drop the rcu lock.
-	 */
-	rcu_read_unlock();
-
-	return queue;
-}
-
-static struct deferred_split *
-folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
-{
-	struct deferred_split *queue;
-
-	rcu_read_lock();
-	queue = split_queue_lock_irqsave(folio_nid(folio), folio_memcg(folio), flags);
-	rcu_read_unlock();
-
-	return queue;
-}
-
-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))
@@ -1293,6 +1189,14 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
 		return NULL;
 	}
+
+	if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
+		folio_put(folio);
+		count_vm_event(THP_FAULT_FALLBACK);
+		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
+		return NULL;
+	}
+
 	folio_throttle_swaprate(folio, gfp);
 
        /*
@@ -3802,33 +3706,25 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
 	struct folio *new_folio, *next;
 	int old_order = folio_order(folio);
 	int ret = 0;
-	struct deferred_split *ds_queue;
+	struct list_lru_one *l;
 
 	VM_WARN_ON_ONCE(!mapping && end);
 	/* Prevent deferred_split_scan() touching ->_refcount */
-	ds_queue = folio_split_queue_lock(folio);
+	l = list_lru_lock(&deferred_split_lru, folio_nid(folio), folio_memcg(folio));
 	if (folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
 		struct swap_cluster_info *ci = NULL;
 		struct lruvec *lruvec;
 
 		if (old_order > 1) {
-			if (!list_empty(&folio->_deferred_list)) {
-				ds_queue->split_queue_len--;
-				/*
-				 * Reinitialize page_deferred_list after removing the
-				 * page from the split_queue, otherwise a subsequent
-				 * split will see list corruption when checking the
-				 * page_deferred_list.
-				 */
-				list_del_init(&folio->_deferred_list);
-			}
+			__list_lru_del(&deferred_split_lru, l,
+				       &folio->_deferred_list, folio_nid(folio));
 			if (folio_test_partially_mapped(folio)) {
 				folio_clear_partially_mapped(folio);
 				mod_mthp_stat(old_order,
 					MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			}
 		}
-		split_queue_unlock(ds_queue);
+		list_lru_unlock(l);
 		if (mapping) {
 			int nr = folio_nr_pages(folio);
 
@@ -3929,7 +3825,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
 		if (ci)
 			swap_cluster_unlock(ci);
 	} else {
-		split_queue_unlock(ds_queue);
+		list_lru_unlock(l);
 		return -EAGAIN;
 	}
 
@@ -4296,33 +4192,35 @@ int split_folio_to_list(struct folio *folio, struct list_head *list)
  * queueing THP splits, and that list is (racily observed to be) non-empty.
  *
  * It is unsafe to call folio_unqueue_deferred_split() until folio refcount is
- * zero: because even when split_queue_lock is held, a non-empty _deferred_list
- * might be in use on deferred_split_scan()'s unlocked on-stack list.
+ * zero: because even when the list_lru lock is held, a non-empty
+ * _deferred_list might be in use on deferred_split_scan()'s unlocked
+ * on-stack list.
  *
- * If memory cgroups are enabled, split_queue_lock is in the mem_cgroup: it is
- * therefore important to unqueue deferred split before changing folio memcg.
+ * The list_lru sublist is determined by folio's memcg: it is therefore
+ * important to unqueue deferred split before changing folio memcg.
  */
 bool __folio_unqueue_deferred_split(struct folio *folio)
 {
-	struct deferred_split *ds_queue;
+	struct list_lru_one *l;
+	int nid = folio_nid(folio);
 	unsigned long flags;
 	bool unqueued = false;
 
 	WARN_ON_ONCE(folio_ref_count(folio));
 	WARN_ON_ONCE(!mem_cgroup_disabled() && !folio_memcg_charged(folio));
 
-	ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
-	if (!list_empty(&folio->_deferred_list)) {
-		ds_queue->split_queue_len--;
+	rcu_read_lock();
+	l = list_lru_lock_irqsave(&deferred_split_lru, nid, folio_memcg(folio), &flags);
+	if (__list_lru_del(&deferred_split_lru, l, &folio->_deferred_list, nid)) {
 		if (folio_test_partially_mapped(folio)) {
 			folio_clear_partially_mapped(folio);
 			mod_mthp_stat(folio_order(folio),
 				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 		}
-		list_del_init(&folio->_deferred_list);
 		unqueued = true;
 	}
-	split_queue_unlock_irqrestore(ds_queue, flags);
+	list_lru_unlock_irqrestore(l, &flags);
+	rcu_read_unlock();
 
 	return unqueued;	/* useful for debug warnings */
 }
@@ -4330,7 +4228,9 @@ 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;
+	struct list_lru_one *l;
+	int nid;
+	struct mem_cgroup *memcg;
 	unsigned long flags;
 
 	/*
@@ -4353,7 +4253,11 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 	if (folio_test_swapcache(folio))
 		return;
 
-	ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
+	nid = folio_nid(folio);
+
+	rcu_read_lock();
+	memcg = folio_memcg(folio);
+	l = list_lru_lock_irqsave(&deferred_split_lru, nid, memcg, &flags);
 	if (partially_mapped) {
 		if (!folio_test_partially_mapped(folio)) {
 			folio_set_partially_mapped(folio);
@@ -4361,36 +4265,20 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 				count_vm_event(THP_DEFERRED_SPLIT_PAGE);
 			count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
 			mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, 1);
-
 		}
 	} else {
 		/* partially mapped folios cannot become non-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++;
-		if (memcg)
-			set_shrinker_bit(memcg, folio_nid(folio),
-					 shrinker_id(deferred_split_shrinker));
-	}
-	split_queue_unlock_irqrestore(ds_queue, flags);
+	__list_lru_add(&deferred_split_lru, l, &folio->_deferred_list, nid, memcg);
+	list_lru_unlock_irqrestore(l, &flags);
+	rcu_read_unlock();
 }
 
 static unsigned long deferred_split_count(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
-	struct pglist_data *pgdata = NODE_DATA(sc->nid);
-	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
-
-#ifdef CONFIG_MEMCG
-	if (sc->memcg)
-		ds_queue = &sc->memcg->deferred_split_queue;
-#endif
-	return READ_ONCE(ds_queue->split_queue_len);
+	return list_lru_shrink_count(&deferred_split_lru, sc);
 }
 
 static bool thp_underused(struct folio *folio)
@@ -4420,45 +4308,47 @@ static bool thp_underused(struct folio *folio)
 	return false;
 }
 
+static enum lru_status deferred_split_isolate(struct list_head *item,
+					      struct list_lru_one *lru,
+					      void *cb_arg)
+{
+	struct folio *folio = container_of(item, struct folio, _deferred_list);
+	struct list_head *freeable = cb_arg;
+
+	if (folio_try_get(folio)) {
+		list_lru_isolate_move(lru, item, freeable);
+		return LRU_REMOVED;
+	}
+
+	/* We lost race with folio_put() */
+	list_lru_isolate(lru, item);
+	if (folio_test_partially_mapped(folio)) {
+		folio_clear_partially_mapped(folio);
+		mod_mthp_stat(folio_order(folio),
+			      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
+	}
+	return LRU_REMOVED;
+}
+
 static unsigned long deferred_split_scan(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
-	struct deferred_split *ds_queue;
-	unsigned long flags;
+	LIST_HEAD(dispose);
 	struct folio *folio, *next;
-	int split = 0, i;
-	struct folio_batch fbatch;
+	int split = 0;
+	unsigned long isolated;
 
-	folio_batch_init(&fbatch);
+	isolated = list_lru_shrink_walk_irq(&deferred_split_lru, sc,
+					    deferred_split_isolate, &dispose);
 
-retry:
-	ds_queue = split_queue_lock_irqsave(sc->nid, sc->memcg, &flags);
-	/* Take pin on all head pages to avoid freeing them under us */
-	list_for_each_entry_safe(folio, next, &ds_queue->split_queue,
-							_deferred_list) {
-		if (folio_try_get(folio)) {
-			folio_batch_add(&fbatch, folio);
-		} else if (folio_test_partially_mapped(folio)) {
-			/* We lost race with folio_put() */
-			folio_clear_partially_mapped(folio);
-			mod_mthp_stat(folio_order(folio),
-				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
-		}
-		list_del_init(&folio->_deferred_list);
-		ds_queue->split_queue_len--;
-		if (!--sc->nr_to_scan)
-			break;
-		if (!folio_batch_space(&fbatch))
-			break;
-	}
-	split_queue_unlock_irqrestore(ds_queue, flags);
-
-	for (i = 0; i < folio_batch_count(&fbatch); i++) {
+	list_for_each_entry_safe(folio, next, &dispose, _deferred_list) {
 		bool did_split = false;
 		bool underused = false;
-		struct deferred_split *fqueue;
+		struct list_lru_one *l;
+		unsigned long flags;
+
+		list_del_init(&folio->_deferred_list);
 
-		folio = fbatch.folios[i];
 		if (!folio_test_partially_mapped(folio)) {
 			/*
 			 * See try_to_map_unused_to_zeropage(): we cannot
@@ -4481,64 +4371,32 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		}
 		folio_unlock(folio);
 next:
-		if (did_split || !folio_test_partially_mapped(folio))
-			continue;
 		/*
 		 * Only add back to the queue if folio is partially mapped.
 		 * If thp_underused returns false, or if split_folio fails
 		 * in the case it was underused, then consider it used and
 		 * don't add it back to split_queue.
 		 */
-		fqueue = folio_split_queue_lock_irqsave(folio, &flags);
-		if (list_empty(&folio->_deferred_list)) {
-			list_add_tail(&folio->_deferred_list, &fqueue->split_queue);
-			fqueue->split_queue_len++;
+		if (!did_split && folio_test_partially_mapped(folio)) {
+			rcu_read_lock();
+			l = list_lru_lock_irqsave(&deferred_split_lru,
+						  folio_nid(folio),
+						  folio_memcg(folio),
+						  &flags);
+			__list_lru_add(&deferred_split_lru, l,
+				       &folio->_deferred_list,
+				       folio_nid(folio), folio_memcg(folio));
+			list_lru_unlock_irqrestore(l, &flags);
+			rcu_read_unlock();
 		}
-		split_queue_unlock_irqrestore(fqueue, flags);
-	}
-	folios_put(&fbatch);
-
-	if (sc->nr_to_scan && !list_empty(&ds_queue->split_queue)) {
-		cond_resched();
-		goto retry;
+		folio_put(folio);
 	}
 
-	/*
-	 * Stop shrinker if we didn't split any page, but the queue is empty.
-	 * This can happen if pages were freed under us.
-	 */
-	if (!split && list_empty(&ds_queue->split_queue))
+	if (!split && !isolated)
 		return SHRINK_STOP;
 	return split;
 }
 
-#ifdef CONFIG_MEMCG
-void reparent_deferred_split_queue(struct mem_cgroup *memcg)
-{
-	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
-	struct deferred_split *ds_queue = &memcg->deferred_split_queue;
-	struct deferred_split *parent_ds_queue = &parent->deferred_split_queue;
-	int nid;
-
-	spin_lock_irq(&ds_queue->split_queue_lock);
-	spin_lock_nested(&parent_ds_queue->split_queue_lock, SINGLE_DEPTH_NESTING);
-
-	if (!ds_queue->split_queue_len)
-		goto unlock;
-
-	list_splice_tail_init(&ds_queue->split_queue, &parent_ds_queue->split_queue);
-	parent_ds_queue->split_queue_len += ds_queue->split_queue_len;
-	ds_queue->split_queue_len = 0;
-
-	for_each_node(nid)
-		set_shrinker_bit(parent, nid, shrinker_id(deferred_split_shrinker));
-
-unlock:
-	spin_unlock(&parent_ds_queue->split_queue_lock);
-	spin_unlock_irq(&ds_queue->split_queue_lock);
-}
-#endif
-
 #ifdef CONFIG_DEBUG_FS
 static void split_huge_pages_all(void)
 {
diff --git a/mm/internal.h b/mm/internal.h
index 95b583e7e4f7..71d2605f8040 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -857,7 +857,7 @@ static inline bool folio_unqueue_deferred_split(struct folio *folio)
 	/*
 	 * At this point, there is no one trying to add the folio to
 	 * deferred_list. If folio is not in deferred_list, it's safe
-	 * to check without acquiring the split_queue_lock.
+	 * to check without acquiring the list_lru lock.
 	 */
 	if (data_race(list_empty(&folio->_deferred_list)))
 		return false;
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b7b4680d27ab..01fd3d5933c5 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1076,6 +1076,7 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru
 	}
 
 	count_vm_event(THP_COLLAPSE_ALLOC);
+
 	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
 		folio_put(folio);
 		*foliop = NULL;
@@ -1084,6 +1085,12 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru
 
 	count_memcg_folio_events(folio, THP_COLLAPSE_ALLOC, 1);
 
+	if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
+		folio_put(folio);
+		*foliop = NULL;
+		return SCAN_CGROUP_CHARGE_FAIL;
+	}
+
 	*foliop = folio;
 	return SCAN_SUCCEED;
 }
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 26463ae29c64..84482dbc673b 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -15,6 +15,28 @@
 #include "slab.h"
 #include "internal.h"
 
+static inline void lock_list_lru(struct list_lru_one *l, bool irq,
+				 unsigned long *irq_flags)
+{
+	if (irq_flags)
+		spin_lock_irqsave(&l->lock, *irq_flags);
+	else if (irq)
+		spin_lock_irq(&l->lock);
+	else
+		spin_lock(&l->lock);
+}
+
+static inline void unlock_list_lru(struct list_lru_one *l, bool irq,
+				   unsigned long *irq_flags)
+{
+	if (irq_flags)
+		spin_unlock_irqrestore(&l->lock, *irq_flags);
+	else if (irq)
+		spin_unlock_irq(&l->lock);
+	else
+		spin_unlock(&l->lock);
+}
+
 #ifdef CONFIG_MEMCG
 static LIST_HEAD(memcg_list_lrus);
 static DEFINE_MUTEX(list_lrus_mutex);
@@ -60,34 +82,22 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
 	return &lru->node[nid].lru;
 }
 
-static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
-{
-	if (irq)
-		spin_lock_irq(&l->lock);
-	else
-		spin_lock(&l->lock);
-	if (unlikely(READ_ONCE(l->nr_items) == LONG_MIN)) {
-		if (irq)
-			spin_unlock_irq(&l->lock);
-		else
-			spin_unlock(&l->lock);
-		return false;
-	}
-	return true;
-}
-
 static inline struct list_lru_one *
 lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
-		       bool irq, bool skip_empty)
+		       bool irq, unsigned long *irq_flags, bool skip_empty)
 {
 	struct list_lru_one *l;
 
 	rcu_read_lock();
 again:
 	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
-	if (likely(l) && lock_list_lru(l, irq)) {
-		rcu_read_unlock();
-		return l;
+	if (likely(l)) {
+		lock_list_lru(l, irq, irq_flags);
+		if (likely(READ_ONCE(l->nr_items) != LONG_MIN)) {
+			rcu_read_unlock();
+			return l;
+		}
+		unlock_list_lru(l, irq, irq_flags);
 	}
 	/*
 	 * Caller may simply bail out if raced with reparenting or
@@ -101,14 +111,6 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 	memcg = parent_mem_cgroup(memcg);
 	goto again;
 }
-
-static inline void unlock_list_lru(struct list_lru_one *l, bool irq_off)
-{
-	if (irq_off)
-		spin_unlock_irq(&l->lock);
-	else
-		spin_unlock(&l->lock);
-}
 #else
 static void list_lru_register(struct list_lru *lru)
 {
@@ -136,48 +138,77 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
 
 static inline struct list_lru_one *
 lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
-		       bool irq, bool skip_empty)
+		       bool irq, unsigned long *irq_flags, bool skip_empty)
 {
 	struct list_lru_one *l = &lru->node[nid].lru;
 
-	if (irq)
-		spin_lock_irq(&l->lock);
-	else
-		spin_lock(&l->lock);
-
+	lock_list_lru(l, irq, irq_flags);
 	return l;
 }
+#endif /* CONFIG_MEMCG */
 
-static inline void unlock_list_lru(struct list_lru_one *l, bool irq_off)
+struct list_lru_one *list_lru_lock(struct list_lru *lru, int nid,
+				   struct mem_cgroup *memcg)
 {
-	if (irq_off)
-		spin_unlock_irq(&l->lock);
-	else
-		spin_unlock(&l->lock);
+	return lock_list_lru_of_memcg(lru, nid, memcg, false, NULL, false);
+}
+
+void list_lru_unlock(struct list_lru_one *l)
+{
+	unlock_list_lru(l, false, NULL);
+}
+
+struct list_lru_one *list_lru_lock_irqsave(struct list_lru *lru, int nid,
+					   struct mem_cgroup *memcg,
+					   unsigned long *irq_flags)
+{
+	return lock_list_lru_of_memcg(lru, nid, memcg, true, irq_flags, false);
+}
+
+void list_lru_unlock_irqrestore(struct list_lru_one *l,
+				unsigned long *irq_flags)
+{
+	unlock_list_lru(l, true, irq_flags);
+}
+
+bool __list_lru_add(struct list_lru *lru, struct list_lru_one *l,
+		    struct list_head *item, int nid,
+		    struct mem_cgroup *memcg)
+{
+	if (!list_empty(item))
+		return false;
+	list_add_tail(item, &l->list);
+	/* Set shrinker bit if the first element was added */
+	if (!l->nr_items++)
+		set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
+	atomic_long_inc(&lru->node[nid].nr_items);
+	return true;
+}
+
+bool __list_lru_del(struct list_lru *lru, struct list_lru_one *l,
+		    struct list_head *item, int nid)
+{
+	if (list_empty(item))
+		return false;
+	list_del_init(item);
+	l->nr_items--;
+	atomic_long_dec(&lru->node[nid].nr_items);
+	return true;
 }
-#endif /* CONFIG_MEMCG */
 
 /* The caller must ensure the memcg lifetime. */
 bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
 		  struct mem_cgroup *memcg)
 {
-	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l;
+	bool ret;
 
-	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
+	l = list_lru_lock(lru, nid, memcg);
 	if (!l)
 		return false;
-	if (list_empty(item)) {
-		list_add_tail(item, &l->list);
-		/* Set shrinker bit if the first element was added */
-		if (!l->nr_items++)
-			set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
-		unlock_list_lru(l, false);
-		atomic_long_inc(&nlru->nr_items);
-		return true;
-	}
-	unlock_list_lru(l, false);
-	return false;
+	ret = __list_lru_add(lru, l, item, nid, memcg);
+	list_lru_unlock(l);
+	return ret;
 }
 
 bool list_lru_add_obj(struct list_lru *lru, struct list_head *item)
@@ -201,20 +232,15 @@ EXPORT_SYMBOL_GPL(list_lru_add_obj);
 bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
 		  struct mem_cgroup *memcg)
 {
-	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l;
-	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
+	bool ret;
+
+	l = list_lru_lock(lru, nid, memcg);
 	if (!l)
 		return false;
-	if (!list_empty(item)) {
-		list_del_init(item);
-		l->nr_items--;
-		unlock_list_lru(l, false);
-		atomic_long_dec(&nlru->nr_items);
-		return true;
-	}
-	unlock_list_lru(l, false);
-	return false;
+	ret = __list_lru_del(lru, l, item, nid);
+	list_lru_unlock(l);
+	return ret;
 }
 
 bool list_lru_del_obj(struct list_lru *lru, struct list_head *item)
@@ -287,7 +313,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 	unsigned long isolated = 0;
 
 restart:
-	l = lock_list_lru_of_memcg(lru, nid, memcg, irq_off, true);
+	l = lock_list_lru_of_memcg(lru, nid, memcg, irq_off, NULL, true);
 	if (!l)
 		return isolated;
 	list_for_each_safe(item, n, &l->list) {
@@ -328,7 +354,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 			BUG();
 		}
 	}
-	unlock_list_lru(l, irq_off);
+	unlock_list_lru(l, irq_off, NULL);
 out:
 	return isolated;
 }
@@ -510,17 +536,14 @@ static inline bool memcg_list_lru_allocated(struct mem_cgroup *memcg,
 	return idx < 0 || xa_load(&lru->xa, idx);
 }
 
-int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
-			 gfp_t gfp)
+static int __memcg_list_lru_alloc(struct mem_cgroup *memcg,
+				  struct list_lru *lru, gfp_t gfp)
 {
 	unsigned long flags;
 	struct list_lru_memcg *mlru = NULL;
 	struct mem_cgroup *pos, *parent;
 	XA_STATE(xas, &lru->xa, 0);
 
-	if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
-		return 0;
-
 	gfp &= GFP_RECLAIM_MASK;
 	/*
 	 * Because the list_lru can be reparented to the parent cgroup's
@@ -561,6 +584,38 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
 
 	return xas_error(&xas);
 }
+
+int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
+			 gfp_t gfp)
+{
+	if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
+		return 0;
+
+	return __memcg_list_lru_alloc(memcg, lru, gfp);
+}
+
+int memcg_list_lru_alloc_folio(struct folio *folio, struct list_lru *lru,
+			       gfp_t gfp)
+{
+	struct mem_cgroup *memcg;
+	int res;
+
+	if (!list_lru_memcg_aware(lru))
+		return 0;
+
+	/* Fast path when list_lru heads already exist */
+	rcu_read_lock();
+	res = memcg_list_lru_allocated(folio_memcg(folio), lru);
+	rcu_read_unlock();
+	if (likely(res))
+		return 0;
+
+	/* Need to allocate, pin the memcg */
+	memcg = get_mem_cgroup_from_folio(folio);
+	res = __memcg_list_lru_alloc(memcg, lru, gfp);
+	mem_cgroup_put(memcg);
+	return res;
+}
 #else
 static inline void memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a47fb68dd65f..f381cb6bdff1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4015,11 +4015,6 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
 	for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++)
 		memcg->cgwb_frn[i].done =
 			__WB_COMPLETION_INIT(&memcg_cgwb_frn_waitq);
-#endif
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	spin_lock_init(&memcg->deferred_split_queue.split_queue_lock);
-	INIT_LIST_HEAD(&memcg->deferred_split_queue.split_queue);
-	memcg->deferred_split_queue.split_queue_len = 0;
 #endif
 	lru_gen_init_memcg(memcg);
 	return memcg;
@@ -4167,11 +4162,10 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 	zswap_memcg_offline_cleanup(memcg);
 
 	memcg_offline_kmem(memcg);
-	reparent_deferred_split_queue(memcg);
 	/*
-	 * The reparenting of objcg must be after the reparenting of the
-	 * list_lru and deferred_split_queue above, which ensures that they will
-	 * not mistakenly get the parent list_lru and deferred_split_queue.
+	 * The reparenting of objcg must be after the reparenting of
+	 * the list_lru in memcg_offline_kmem(), which ensures that
+	 * they will not mistakenly get the parent list_lru.
 	 */
 	memcg_reparent_objcgs(memcg);
 	reparent_shrinker_deferred(memcg);
diff --git a/mm/memory.c b/mm/memory.c
index 38062f8e1165..4dad1a7890aa 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4651,13 +4651,19 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
 	while (orders) {
 		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
 		folio = vma_alloc_folio(gfp, order, vma, addr);
-		if (folio) {
-			if (!mem_cgroup_swapin_charge_folio(folio, vma->vm_mm,
-							    gfp, entry))
-				return folio;
+		if (!folio)
+			goto next;
+		if (mem_cgroup_swapin_charge_folio(folio, vma->vm_mm, gfp, entry)) {
 			count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK_CHARGE);
 			folio_put(folio);
+			goto next;
 		}
+		if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
+			folio_put(folio);
+			goto fallback;
+		}
+		return folio;
+next:
 		count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
 		order = next_order(&orders, order);
 	}
@@ -5168,24 +5174,28 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 	while (orders) {
 		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
 		folio = vma_alloc_folio(gfp, order, vma, addr);
-		if (folio) {
-			if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
-				count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
-				folio_put(folio);
-				goto next;
-			}
-			folio_throttle_swaprate(folio, gfp);
-			/*
-			 * When a folio is not zeroed during allocation
-			 * (__GFP_ZERO not used) or user folios require special
-			 * handling, folio_zero_user() is used to make sure
-			 * that the page corresponding to the faulting address
-			 * will be hot in the cache after zeroing.
-			 */
-			if (user_alloc_needs_zeroing())
-				folio_zero_user(folio, vmf->address);
-			return folio;
+		if (!folio)
+			goto next;
+		if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
+			count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
+			folio_put(folio);
+			goto next;
 		}
+		if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
+			folio_put(folio);
+			goto fallback;
+		}
+		folio_throttle_swaprate(folio, gfp);
+		/*
+		 * When a folio is not zeroed during allocation
+		 * (__GFP_ZERO not used) or user folios require special
+		 * handling, folio_zero_user() is used to make sure
+		 * that the page corresponding to the faulting address
+		 * will be hot in the cache after zeroing.
+		 */
+		if (user_alloc_needs_zeroing())
+			folio_zero_user(folio, vmf->address);
+		return folio;
 next:
 		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
 		order = next_order(&orders, order);
diff --git a/mm/mm_init.c b/mm/mm_init.c
index cec7bb758bdd..ed357e73b7e9 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1388,19 +1388,6 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 	pr_debug("On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
 }
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-static void pgdat_init_split_queue(struct pglist_data *pgdat)
-{
-	struct deferred_split *ds_queue = &pgdat->deferred_split_queue;
-
-	spin_lock_init(&ds_queue->split_queue_lock);
-	INIT_LIST_HEAD(&ds_queue->split_queue);
-	ds_queue->split_queue_len = 0;
-}
-#else
-static void pgdat_init_split_queue(struct pglist_data *pgdat) {}
-#endif
-
 #ifdef CONFIG_COMPACTION
 static void pgdat_init_kcompactd(struct pglist_data *pgdat)
 {
@@ -1417,7 +1404,6 @@ static void __meminit pgdat_init_internals(struct pglist_data *pgdat)
 	pgdat_resize_init(pgdat);
 	pgdat_kswapd_lock_init(pgdat);
 
-	pgdat_init_split_queue(pgdat);
 	pgdat_init_kcompactd(pgdat);
 
 	init_waitqueue_head(&pgdat->kswapd_wait);
-- 
2.53.0

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Johannes Weiner]

Fixing David's email address. Sorry! Full quote below.

On Wed, Mar 11, 2026 at 11:43:58AM -0400, Johannes Weiner wrote:
> The deferred split queue handles cgroups in a suboptimal fashion. The
> queue is per-NUMA node or per-cgroup, not the intersection. That means
> on a cgrouped system, a node-restricted allocation entering reclaim
> can end up splitting large pages on other nodes:
> 
> 	alloc/unmap
> 	  deferred_split_folio()
> 	    list_add_tail(memcg->split_queue)
> 	    set_shrinker_bit(memcg, node, deferred_shrinker_id)
> 
> 	for_each_zone_zonelist_nodemask(restricted_nodes)
> 	  mem_cgroup_iter()
> 	    shrink_slab(node, memcg)
> 	      shrink_slab_memcg(node, memcg)
> 	        if test_shrinker_bit(memcg, node, deferred_shrinker_id)
> 	          deferred_split_scan()
> 	            walks memcg->split_queue
> 
> The shrinker bit adds an imperfect guard rail. As soon as the cgroup
> has a single large page on the node of interest, all large pages owned
> by that memcg, including those on other nodes, will be split.
> 
> list_lru properly sets up per-node, per-cgroup lists. As a bonus, it
> streamlines a lot of the list operations and reclaim walks. It's used
> widely by other major shrinkers already. Convert the deferred split
> queue as well.
> 
> The list_lru per-memcg heads are instantiated on demand when the first
> object of interest is allocated for a cgroup, by calling
> memcg_list_lru_alloc(). Add calls to where splittable pages are
> created: anon faults, swapin faults, khugepaged collapse.
> 
> These calls create all possible node heads for the cgroup at once, so
> the migration code (between nodes) doesn't need any special care.
> 
> The folio_test_partially_mapped() state is currently protected and
> serialized wrt LRU state by the deferred split queue lock. To
> facilitate the transition, add helpers to the list_lru API to allow
> caller-side locking.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/huge_mm.h    |   6 +-
>  include/linux/list_lru.h   |  48 ++++++
>  include/linux/memcontrol.h |   4 -
>  include/linux/mmzone.h     |  12 --
>  mm/huge_memory.c           | 326 +++++++++++--------------------------
>  mm/internal.h              |   2 +-
>  mm/khugepaged.c            |   7 +
>  mm/list_lru.c              | 197 ++++++++++++++--------
>  mm/memcontrol.c            |  12 +-
>  mm/memory.c                |  52 +++---
>  mm/mm_init.c               |  14 --
>  11 files changed, 310 insertions(+), 370 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index a4d9f964dfde..2d0d0c797dd8 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -414,10 +414,9 @@ static inline int split_huge_page(struct page *page)
>  {
>  	return split_huge_page_to_list_to_order(page, NULL, 0);
>  }
> +
> +extern struct list_lru deferred_split_lru;
>  void deferred_split_folio(struct folio *folio, bool partially_mapped);
> -#ifdef CONFIG_MEMCG
> -void reparent_deferred_split_queue(struct mem_cgroup *memcg);
> -#endif
>  
>  void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>  		unsigned long address, bool freeze);
> @@ -650,7 +649,6 @@ static inline int try_folio_split_to_order(struct folio *folio,
>  }
>  
>  static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
> -static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {}
>  #define split_huge_pmd(__vma, __pmd, __address)	\
>  	do { } while (0)
>  
> diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> index fe739d35a864..d75f25778ba1 100644
> --- a/include/linux/list_lru.h
> +++ b/include/linux/list_lru.h
> @@ -81,8 +81,56 @@ static inline int list_lru_init_memcg_key(struct list_lru *lru, struct shrinker
>  
>  int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
>  			 gfp_t gfp);
> +
> +#ifdef CONFIG_MEMCG
> +int memcg_list_lru_alloc_folio(struct folio *folio, struct list_lru *lru,
> +			       gfp_t gfp);
> +#else
> +static inline int memcg_list_lru_alloc_folio(struct folio *folio,
> +					     struct list_lru *lru, gfp_t gfp)
> +{
> +	return 0;
> +}
> +#endif
> +
>  void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *parent);
>  
> +/**
> + * list_lru_lock: lock the sublist for the given node and memcg
> + * @lru: the lru pointer
> + * @nid: the node id of the sublist to lock.
> + * @memcg: the cgroup of the sublist to lock.
> + *
> + * Returns the locked list_lru_one sublist. The caller must call
> + * list_lru_unlock() when done.
> + *
> + * You must ensure that the memcg is not freed during this call (e.g., with
> + * rcu or by taking a css refcnt).
> + *
> + * Return: the locked list_lru_one, or NULL on failure
> + */
> +struct list_lru_one *list_lru_lock(struct list_lru *lru, int nid,
> +				   struct mem_cgroup *memcg);
> +
> +/**
> + * list_lru_unlock: unlock a sublist locked by list_lru_lock()
> + * @l: the list_lru_one to unlock
> + */
> +void list_lru_unlock(struct list_lru_one *l);
> +
> +struct list_lru_one *list_lru_lock_irqsave(struct list_lru *lru, int nid,
> +					   struct mem_cgroup *memcg,
> +					   unsigned long *irq_flags);
> +void list_lru_unlock_irqrestore(struct list_lru_one *l,
> +				unsigned long *irq_flags);
> +
> +/* Caller-locked variants, see list_lru_add() etc for documentation */
> +bool __list_lru_add(struct list_lru *lru, struct list_lru_one *l,
> +		    struct list_head *item, int nid,
> +		    struct mem_cgroup *memcg);
> +bool __list_lru_del(struct list_lru *lru, struct list_lru_one *l,
> +		    struct list_head *item, int nid);
> +
>  /**
>   * list_lru_add: add an element to the lru list's tail
>   * @lru: the lru pointer
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 086158969529..0782c72a1997 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -277,10 +277,6 @@ struct mem_cgroup {
>  	struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT];
>  #endif
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	struct deferred_split deferred_split_queue;
> -#endif
> -
>  #ifdef CONFIG_LRU_GEN_WALKS_MMU
>  	/* per-memcg mm_struct list */
>  	struct lru_gen_mm_list mm_list;
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 7bd0134c241c..232b7a71fd69 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1429,14 +1429,6 @@ struct zonelist {
>   */
>  extern struct page *mem_map;
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -struct deferred_split {
> -	spinlock_t split_queue_lock;
> -	struct list_head split_queue;
> -	unsigned long split_queue_len;
> -};
> -#endif
> -
>  #ifdef CONFIG_MEMORY_FAILURE
>  /*
>   * Per NUMA node memory failure handling statistics.
> @@ -1562,10 +1554,6 @@ typedef struct pglist_data {
>  	unsigned long first_deferred_pfn;
>  #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	struct deferred_split deferred_split_queue;
> -#endif
> -
>  #ifdef CONFIG_NUMA_BALANCING
>  	/* start time in ms of current promote rate limit period */
>  	unsigned int nbp_rl_start;
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 7d0a64033b18..f43051eaf089 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -14,6 +14,7 @@
>  #include <linux/mmu_notifier.h>
>  #include <linux/rmap.h>
>  #include <linux/swap.h>
> +#include <linux/list_lru.h>
>  #include <linux/shrinker.h>
>  #include <linux/mm_inline.h>
>  #include <linux/swapops.h>
> @@ -67,6 +68,7 @@ unsigned long transparent_hugepage_flags __read_mostly =
>  	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
>  	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
>  
> +struct list_lru deferred_split_lru;
>  static struct shrinker *deferred_split_shrinker;
>  static unsigned long deferred_split_count(struct shrinker *shrink,
>  					  struct shrink_control *sc);
> @@ -866,6 +868,11 @@ static int __init thp_shrinker_init(void)
>  	if (!deferred_split_shrinker)
>  		return -ENOMEM;
>  
> +	if (list_lru_init_memcg(&deferred_split_lru, deferred_split_shrinker)) {
> +		shrinker_free(deferred_split_shrinker);
> +		return -ENOMEM;
> +	}
> +
>  	deferred_split_shrinker->count_objects = deferred_split_count;
>  	deferred_split_shrinker->scan_objects = deferred_split_scan;
>  	shrinker_register(deferred_split_shrinker);
> @@ -886,6 +893,7 @@ static int __init thp_shrinker_init(void)
>  
>  	huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero");
>  	if (!huge_zero_folio_shrinker) {
> +		list_lru_destroy(&deferred_split_lru);
>  		shrinker_free(deferred_split_shrinker);
>  		return -ENOMEM;
>  	}
> @@ -900,6 +908,7 @@ static int __init thp_shrinker_init(void)
>  static void __init thp_shrinker_exit(void)
>  {
>  	shrinker_free(huge_zero_folio_shrinker);
> +	list_lru_destroy(&deferred_split_lru);
>  	shrinker_free(deferred_split_shrinker);
>  }
>  
> @@ -1080,119 +1089,6 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
>  	return pmd;
>  }
>  
> -static struct deferred_split *split_queue_node(int nid)
> -{
> -	struct pglist_data *pgdata = NODE_DATA(nid);
> -
> -	return &pgdata->deferred_split_queue;
> -}
> -
> -#ifdef CONFIG_MEMCG
> -static inline
> -struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
> -					   struct deferred_split *queue)
> -{
> -	if (mem_cgroup_disabled())
> -		return NULL;
> -	if (split_queue_node(folio_nid(folio)) == queue)
> -		return NULL;
> -	return container_of(queue, struct mem_cgroup, deferred_split_queue);
> -}
> -
> -static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memcg)
> -{
> -	return memcg ? &memcg->deferred_split_queue : split_queue_node(nid);
> -}
> -#else
> -static inline
> -struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
> -					   struct deferred_split *queue)
> -{
> -	return NULL;
> -}
> -
> -static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memcg)
> -{
> -	return split_queue_node(nid);
> -}
> -#endif
> -
> -static struct deferred_split *split_queue_lock(int nid, struct mem_cgroup *memcg)
> -{
> -	struct deferred_split *queue;
> -
> -retry:
> -	queue = memcg_split_queue(nid, memcg);
> -	spin_lock(&queue->split_queue_lock);
> -	/*
> -	 * There is a period between setting memcg to dying and reparenting
> -	 * deferred split queue, and during this period the THPs in the deferred
> -	 * split queue will be hidden from the shrinker side.
> -	 */
> -	if (unlikely(memcg_is_dying(memcg))) {
> -		spin_unlock(&queue->split_queue_lock);
> -		memcg = parent_mem_cgroup(memcg);
> -		goto retry;
> -	}
> -
> -	return queue;
> -}
> -
> -static struct deferred_split *
> -split_queue_lock_irqsave(int nid, struct mem_cgroup *memcg, unsigned long *flags)
> -{
> -	struct deferred_split *queue;
> -
> -retry:
> -	queue = memcg_split_queue(nid, memcg);
> -	spin_lock_irqsave(&queue->split_queue_lock, *flags);
> -	if (unlikely(memcg_is_dying(memcg))) {
> -		spin_unlock_irqrestore(&queue->split_queue_lock, *flags);
> -		memcg = parent_mem_cgroup(memcg);
> -		goto retry;
> -	}
> -
> -	return queue;
> -}
> -
> -static struct deferred_split *folio_split_queue_lock(struct folio *folio)
> -{
> -	struct deferred_split *queue;
> -
> -	rcu_read_lock();
> -	queue = split_queue_lock(folio_nid(folio), folio_memcg(folio));
> -	/*
> -	 * The memcg destruction path is acquiring the split queue lock for
> -	 * reparenting. Once you have it locked, it's safe to drop the rcu lock.
> -	 */
> -	rcu_read_unlock();
> -
> -	return queue;
> -}
> -
> -static struct deferred_split *
> -folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
> -{
> -	struct deferred_split *queue;
> -
> -	rcu_read_lock();
> -	queue = split_queue_lock_irqsave(folio_nid(folio), folio_memcg(folio), flags);
> -	rcu_read_unlock();
> -
> -	return queue;
> -}
> -
> -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))
> @@ -1293,6 +1189,14 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
>  		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
>  		return NULL;
>  	}
> +
> +	if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
> +		folio_put(folio);
> +		count_vm_event(THP_FAULT_FALLBACK);
> +		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
> +		return NULL;
> +	}
> +
>  	folio_throttle_swaprate(folio, gfp);
>  
>         /*
> @@ -3802,33 +3706,25 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>  	struct folio *new_folio, *next;
>  	int old_order = folio_order(folio);
>  	int ret = 0;
> -	struct deferred_split *ds_queue;
> +	struct list_lru_one *l;
>  
>  	VM_WARN_ON_ONCE(!mapping && end);
>  	/* Prevent deferred_split_scan() touching ->_refcount */
> -	ds_queue = folio_split_queue_lock(folio);
> +	l = list_lru_lock(&deferred_split_lru, folio_nid(folio), folio_memcg(folio));
>  	if (folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
>  		struct swap_cluster_info *ci = NULL;
>  		struct lruvec *lruvec;
>  
>  		if (old_order > 1) {
> -			if (!list_empty(&folio->_deferred_list)) {
> -				ds_queue->split_queue_len--;
> -				/*
> -				 * Reinitialize page_deferred_list after removing the
> -				 * page from the split_queue, otherwise a subsequent
> -				 * split will see list corruption when checking the
> -				 * page_deferred_list.
> -				 */
> -				list_del_init(&folio->_deferred_list);
> -			}
> +			__list_lru_del(&deferred_split_lru, l,
> +				       &folio->_deferred_list, folio_nid(folio));
>  			if (folio_test_partially_mapped(folio)) {
>  				folio_clear_partially_mapped(folio);
>  				mod_mthp_stat(old_order,
>  					MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
>  			}
>  		}
> -		split_queue_unlock(ds_queue);
> +		list_lru_unlock(l);
>  		if (mapping) {
>  			int nr = folio_nr_pages(folio);
>  
> @@ -3929,7 +3825,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>  		if (ci)
>  			swap_cluster_unlock(ci);
>  	} else {
> -		split_queue_unlock(ds_queue);
> +		list_lru_unlock(l);
>  		return -EAGAIN;
>  	}
>  
> @@ -4296,33 +4192,35 @@ int split_folio_to_list(struct folio *folio, struct list_head *list)
>   * queueing THP splits, and that list is (racily observed to be) non-empty.
>   *
>   * It is unsafe to call folio_unqueue_deferred_split() until folio refcount is
> - * zero: because even when split_queue_lock is held, a non-empty _deferred_list
> - * might be in use on deferred_split_scan()'s unlocked on-stack list.
> + * zero: because even when the list_lru lock is held, a non-empty
> + * _deferred_list might be in use on deferred_split_scan()'s unlocked
> + * on-stack list.
>   *
> - * If memory cgroups are enabled, split_queue_lock is in the mem_cgroup: it is
> - * therefore important to unqueue deferred split before changing folio memcg.
> + * The list_lru sublist is determined by folio's memcg: it is therefore
> + * important to unqueue deferred split before changing folio memcg.
>   */
>  bool __folio_unqueue_deferred_split(struct folio *folio)
>  {
> -	struct deferred_split *ds_queue;
> +	struct list_lru_one *l;
> +	int nid = folio_nid(folio);
>  	unsigned long flags;
>  	bool unqueued = false;
>  
>  	WARN_ON_ONCE(folio_ref_count(folio));
>  	WARN_ON_ONCE(!mem_cgroup_disabled() && !folio_memcg_charged(folio));
>  
> -	ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
> -	if (!list_empty(&folio->_deferred_list)) {
> -		ds_queue->split_queue_len--;
> +	rcu_read_lock();
> +	l = list_lru_lock_irqsave(&deferred_split_lru, nid, folio_memcg(folio), &flags);
> +	if (__list_lru_del(&deferred_split_lru, l, &folio->_deferred_list, nid)) {
>  		if (folio_test_partially_mapped(folio)) {
>  			folio_clear_partially_mapped(folio);
>  			mod_mthp_stat(folio_order(folio),
>  				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
>  		}
> -		list_del_init(&folio->_deferred_list);
>  		unqueued = true;
>  	}
> -	split_queue_unlock_irqrestore(ds_queue, flags);
> +	list_lru_unlock_irqrestore(l, &flags);
> +	rcu_read_unlock();
>  
>  	return unqueued;	/* useful for debug warnings */
>  }
> @@ -4330,7 +4228,9 @@ 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;
> +	struct list_lru_one *l;
> +	int nid;
> +	struct mem_cgroup *memcg;
>  	unsigned long flags;
>  
>  	/*
> @@ -4353,7 +4253,11 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
>  	if (folio_test_swapcache(folio))
>  		return;
>  
> -	ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
> +	nid = folio_nid(folio);
> +
> +	rcu_read_lock();
> +	memcg = folio_memcg(folio);
> +	l = list_lru_lock_irqsave(&deferred_split_lru, nid, memcg, &flags);
>  	if (partially_mapped) {
>  		if (!folio_test_partially_mapped(folio)) {
>  			folio_set_partially_mapped(folio);
> @@ -4361,36 +4265,20 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
>  				count_vm_event(THP_DEFERRED_SPLIT_PAGE);
>  			count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
>  			mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, 1);
> -
>  		}
>  	} else {
>  		/* partially mapped folios cannot become non-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++;
> -		if (memcg)
> -			set_shrinker_bit(memcg, folio_nid(folio),
> -					 shrinker_id(deferred_split_shrinker));
> -	}
> -	split_queue_unlock_irqrestore(ds_queue, flags);
> +	__list_lru_add(&deferred_split_lru, l, &folio->_deferred_list, nid, memcg);
> +	list_lru_unlock_irqrestore(l, &flags);
> +	rcu_read_unlock();
>  }
>  
>  static unsigned long deferred_split_count(struct shrinker *shrink,
>  		struct shrink_control *sc)
>  {
> -	struct pglist_data *pgdata = NODE_DATA(sc->nid);
> -	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
> -
> -#ifdef CONFIG_MEMCG
> -	if (sc->memcg)
> -		ds_queue = &sc->memcg->deferred_split_queue;
> -#endif
> -	return READ_ONCE(ds_queue->split_queue_len);
> +	return list_lru_shrink_count(&deferred_split_lru, sc);
>  }
>  
>  static bool thp_underused(struct folio *folio)
> @@ -4420,45 +4308,47 @@ static bool thp_underused(struct folio *folio)
>  	return false;
>  }
>  
> +static enum lru_status deferred_split_isolate(struct list_head *item,
> +					      struct list_lru_one *lru,
> +					      void *cb_arg)
> +{
> +	struct folio *folio = container_of(item, struct folio, _deferred_list);
> +	struct list_head *freeable = cb_arg;
> +
> +	if (folio_try_get(folio)) {
> +		list_lru_isolate_move(lru, item, freeable);
> +		return LRU_REMOVED;
> +	}
> +
> +	/* We lost race with folio_put() */
> +	list_lru_isolate(lru, item);
> +	if (folio_test_partially_mapped(folio)) {
> +		folio_clear_partially_mapped(folio);
> +		mod_mthp_stat(folio_order(folio),
> +			      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
> +	}
> +	return LRU_REMOVED;
> +}
> +
>  static unsigned long deferred_split_scan(struct shrinker *shrink,
>  		struct shrink_control *sc)
>  {
> -	struct deferred_split *ds_queue;
> -	unsigned long flags;
> +	LIST_HEAD(dispose);
>  	struct folio *folio, *next;
> -	int split = 0, i;
> -	struct folio_batch fbatch;
> +	int split = 0;
> +	unsigned long isolated;
>  
> -	folio_batch_init(&fbatch);
> +	isolated = list_lru_shrink_walk_irq(&deferred_split_lru, sc,
> +					    deferred_split_isolate, &dispose);
>  
> -retry:
> -	ds_queue = split_queue_lock_irqsave(sc->nid, sc->memcg, &flags);
> -	/* Take pin on all head pages to avoid freeing them under us */
> -	list_for_each_entry_safe(folio, next, &ds_queue->split_queue,
> -							_deferred_list) {
> -		if (folio_try_get(folio)) {
> -			folio_batch_add(&fbatch, folio);
> -		} else if (folio_test_partially_mapped(folio)) {
> -			/* We lost race with folio_put() */
> -			folio_clear_partially_mapped(folio);
> -			mod_mthp_stat(folio_order(folio),
> -				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
> -		}
> -		list_del_init(&folio->_deferred_list);
> -		ds_queue->split_queue_len--;
> -		if (!--sc->nr_to_scan)
> -			break;
> -		if (!folio_batch_space(&fbatch))
> -			break;
> -	}
> -	split_queue_unlock_irqrestore(ds_queue, flags);
> -
> -	for (i = 0; i < folio_batch_count(&fbatch); i++) {
> +	list_for_each_entry_safe(folio, next, &dispose, _deferred_list) {
>  		bool did_split = false;
>  		bool underused = false;
> -		struct deferred_split *fqueue;
> +		struct list_lru_one *l;
> +		unsigned long flags;
> +
> +		list_del_init(&folio->_deferred_list);
>  
> -		folio = fbatch.folios[i];
>  		if (!folio_test_partially_mapped(folio)) {
>  			/*
>  			 * See try_to_map_unused_to_zeropage(): we cannot
> @@ -4481,64 +4371,32 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>  		}
>  		folio_unlock(folio);
>  next:
> -		if (did_split || !folio_test_partially_mapped(folio))
> -			continue;
>  		/*
>  		 * Only add back to the queue if folio is partially mapped.
>  		 * If thp_underused returns false, or if split_folio fails
>  		 * in the case it was underused, then consider it used and
>  		 * don't add it back to split_queue.
>  		 */
> -		fqueue = folio_split_queue_lock_irqsave(folio, &flags);
> -		if (list_empty(&folio->_deferred_list)) {
> -			list_add_tail(&folio->_deferred_list, &fqueue->split_queue);
> -			fqueue->split_queue_len++;
> +		if (!did_split && folio_test_partially_mapped(folio)) {
> +			rcu_read_lock();
> +			l = list_lru_lock_irqsave(&deferred_split_lru,
> +						  folio_nid(folio),
> +						  folio_memcg(folio),
> +						  &flags);
> +			__list_lru_add(&deferred_split_lru, l,
> +				       &folio->_deferred_list,
> +				       folio_nid(folio), folio_memcg(folio));
> +			list_lru_unlock_irqrestore(l, &flags);
> +			rcu_read_unlock();
>  		}
> -		split_queue_unlock_irqrestore(fqueue, flags);
> -	}
> -	folios_put(&fbatch);
> -
> -	if (sc->nr_to_scan && !list_empty(&ds_queue->split_queue)) {
> -		cond_resched();
> -		goto retry;
> +		folio_put(folio);
>  	}
>  
> -	/*
> -	 * Stop shrinker if we didn't split any page, but the queue is empty.
> -	 * This can happen if pages were freed under us.
> -	 */
> -	if (!split && list_empty(&ds_queue->split_queue))
> +	if (!split && !isolated)
>  		return SHRINK_STOP;
>  	return split;
>  }
>  
> -#ifdef CONFIG_MEMCG
> -void reparent_deferred_split_queue(struct mem_cgroup *memcg)
> -{
> -	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
> -	struct deferred_split *ds_queue = &memcg->deferred_split_queue;
> -	struct deferred_split *parent_ds_queue = &parent->deferred_split_queue;
> -	int nid;
> -
> -	spin_lock_irq(&ds_queue->split_queue_lock);
> -	spin_lock_nested(&parent_ds_queue->split_queue_lock, SINGLE_DEPTH_NESTING);
> -
> -	if (!ds_queue->split_queue_len)
> -		goto unlock;
> -
> -	list_splice_tail_init(&ds_queue->split_queue, &parent_ds_queue->split_queue);
> -	parent_ds_queue->split_queue_len += ds_queue->split_queue_len;
> -	ds_queue->split_queue_len = 0;
> -
> -	for_each_node(nid)
> -		set_shrinker_bit(parent, nid, shrinker_id(deferred_split_shrinker));
> -
> -unlock:
> -	spin_unlock(&parent_ds_queue->split_queue_lock);
> -	spin_unlock_irq(&ds_queue->split_queue_lock);
> -}
> -#endif
> -
>  #ifdef CONFIG_DEBUG_FS
>  static void split_huge_pages_all(void)
>  {
> diff --git a/mm/internal.h b/mm/internal.h
> index 95b583e7e4f7..71d2605f8040 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -857,7 +857,7 @@ static inline bool folio_unqueue_deferred_split(struct folio *folio)
>  	/*
>  	 * At this point, there is no one trying to add the folio to
>  	 * deferred_list. If folio is not in deferred_list, it's safe
> -	 * to check without acquiring the split_queue_lock.
> +	 * to check without acquiring the list_lru lock.
>  	 */
>  	if (data_race(list_empty(&folio->_deferred_list)))
>  		return false;
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b7b4680d27ab..01fd3d5933c5 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1076,6 +1076,7 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru
>  	}
>  
>  	count_vm_event(THP_COLLAPSE_ALLOC);
> +
>  	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
>  		folio_put(folio);
>  		*foliop = NULL;
> @@ -1084,6 +1085,12 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru
>  
>  	count_memcg_folio_events(folio, THP_COLLAPSE_ALLOC, 1);
>  
> +	if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
> +		folio_put(folio);
> +		*foliop = NULL;
> +		return SCAN_CGROUP_CHARGE_FAIL;
> +	}
> +
>  	*foliop = folio;
>  	return SCAN_SUCCEED;
>  }
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 26463ae29c64..84482dbc673b 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -15,6 +15,28 @@
>  #include "slab.h"
>  #include "internal.h"
>  
> +static inline void lock_list_lru(struct list_lru_one *l, bool irq,
> +				 unsigned long *irq_flags)
> +{
> +	if (irq_flags)
> +		spin_lock_irqsave(&l->lock, *irq_flags);
> +	else if (irq)
> +		spin_lock_irq(&l->lock);
> +	else
> +		spin_lock(&l->lock);
> +}
> +
> +static inline void unlock_list_lru(struct list_lru_one *l, bool irq,
> +				   unsigned long *irq_flags)
> +{
> +	if (irq_flags)
> +		spin_unlock_irqrestore(&l->lock, *irq_flags);
> +	else if (irq)
> +		spin_unlock_irq(&l->lock);
> +	else
> +		spin_unlock(&l->lock);
> +}
> +
>  #ifdef CONFIG_MEMCG
>  static LIST_HEAD(memcg_list_lrus);
>  static DEFINE_MUTEX(list_lrus_mutex);
> @@ -60,34 +82,22 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
>  	return &lru->node[nid].lru;
>  }
>  
> -static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
> -{
> -	if (irq)
> -		spin_lock_irq(&l->lock);
> -	else
> -		spin_lock(&l->lock);
> -	if (unlikely(READ_ONCE(l->nr_items) == LONG_MIN)) {
> -		if (irq)
> -			spin_unlock_irq(&l->lock);
> -		else
> -			spin_unlock(&l->lock);
> -		return false;
> -	}
> -	return true;
> -}
> -
>  static inline struct list_lru_one *
>  lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
> -		       bool irq, bool skip_empty)
> +		       bool irq, unsigned long *irq_flags, bool skip_empty)
>  {
>  	struct list_lru_one *l;
>  
>  	rcu_read_lock();
>  again:
>  	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
> -	if (likely(l) && lock_list_lru(l, irq)) {
> -		rcu_read_unlock();
> -		return l;
> +	if (likely(l)) {
> +		lock_list_lru(l, irq, irq_flags);
> +		if (likely(READ_ONCE(l->nr_items) != LONG_MIN)) {
> +			rcu_read_unlock();
> +			return l;
> +		}
> +		unlock_list_lru(l, irq, irq_flags);
>  	}
>  	/*
>  	 * Caller may simply bail out if raced with reparenting or
> @@ -101,14 +111,6 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  	memcg = parent_mem_cgroup(memcg);
>  	goto again;
>  }
> -
> -static inline void unlock_list_lru(struct list_lru_one *l, bool irq_off)
> -{
> -	if (irq_off)
> -		spin_unlock_irq(&l->lock);
> -	else
> -		spin_unlock(&l->lock);
> -}
>  #else
>  static void list_lru_register(struct list_lru *lru)
>  {
> @@ -136,48 +138,77 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
>  
>  static inline struct list_lru_one *
>  lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
> -		       bool irq, bool skip_empty)
> +		       bool irq, unsigned long *irq_flags, bool skip_empty)
>  {
>  	struct list_lru_one *l = &lru->node[nid].lru;
>  
> -	if (irq)
> -		spin_lock_irq(&l->lock);
> -	else
> -		spin_lock(&l->lock);
> -
> +	lock_list_lru(l, irq, irq_flags);
>  	return l;
>  }
> +#endif /* CONFIG_MEMCG */
>  
> -static inline void unlock_list_lru(struct list_lru_one *l, bool irq_off)
> +struct list_lru_one *list_lru_lock(struct list_lru *lru, int nid,
> +				   struct mem_cgroup *memcg)
>  {
> -	if (irq_off)
> -		spin_unlock_irq(&l->lock);
> -	else
> -		spin_unlock(&l->lock);
> +	return lock_list_lru_of_memcg(lru, nid, memcg, false, NULL, false);
> +}
> +
> +void list_lru_unlock(struct list_lru_one *l)
> +{
> +	unlock_list_lru(l, false, NULL);
> +}
> +
> +struct list_lru_one *list_lru_lock_irqsave(struct list_lru *lru, int nid,
> +					   struct mem_cgroup *memcg,
> +					   unsigned long *irq_flags)
> +{
> +	return lock_list_lru_of_memcg(lru, nid, memcg, true, irq_flags, false);
> +}
> +
> +void list_lru_unlock_irqrestore(struct list_lru_one *l,
> +				unsigned long *irq_flags)
> +{
> +	unlock_list_lru(l, true, irq_flags);
> +}
> +
> +bool __list_lru_add(struct list_lru *lru, struct list_lru_one *l,
> +		    struct list_head *item, int nid,
> +		    struct mem_cgroup *memcg)
> +{
> +	if (!list_empty(item))
> +		return false;
> +	list_add_tail(item, &l->list);
> +	/* Set shrinker bit if the first element was added */
> +	if (!l->nr_items++)
> +		set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
> +	atomic_long_inc(&lru->node[nid].nr_items);
> +	return true;
> +}
> +
> +bool __list_lru_del(struct list_lru *lru, struct list_lru_one *l,
> +		    struct list_head *item, int nid)
> +{
> +	if (list_empty(item))
> +		return false;
> +	list_del_init(item);
> +	l->nr_items--;
> +	atomic_long_dec(&lru->node[nid].nr_items);
> +	return true;
>  }
> -#endif /* CONFIG_MEMCG */
>  
>  /* The caller must ensure the memcg lifetime. */
>  bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
>  		  struct mem_cgroup *memcg)
>  {
> -	struct list_lru_node *nlru = &lru->node[nid];
>  	struct list_lru_one *l;
> +	bool ret;
>  
> -	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> +	l = list_lru_lock(lru, nid, memcg);
>  	if (!l)
>  		return false;
> -	if (list_empty(item)) {
> -		list_add_tail(item, &l->list);
> -		/* Set shrinker bit if the first element was added */
> -		if (!l->nr_items++)
> -			set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
> -		unlock_list_lru(l, false);
> -		atomic_long_inc(&nlru->nr_items);
> -		return true;
> -	}
> -	unlock_list_lru(l, false);
> -	return false;
> +	ret = __list_lru_add(lru, l, item, nid, memcg);
> +	list_lru_unlock(l);
> +	return ret;
>  }
>  
>  bool list_lru_add_obj(struct list_lru *lru, struct list_head *item)
> @@ -201,20 +232,15 @@ EXPORT_SYMBOL_GPL(list_lru_add_obj);
>  bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
>  		  struct mem_cgroup *memcg)
>  {
> -	struct list_lru_node *nlru = &lru->node[nid];
>  	struct list_lru_one *l;
> -	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> +	bool ret;
> +
> +	l = list_lru_lock(lru, nid, memcg);
>  	if (!l)
>  		return false;
> -	if (!list_empty(item)) {
> -		list_del_init(item);
> -		l->nr_items--;
> -		unlock_list_lru(l, false);
> -		atomic_long_dec(&nlru->nr_items);
> -		return true;
> -	}
> -	unlock_list_lru(l, false);
> -	return false;
> +	ret = __list_lru_del(lru, l, item, nid);
> +	list_lru_unlock(l);
> +	return ret;
>  }
>  
>  bool list_lru_del_obj(struct list_lru *lru, struct list_head *item)
> @@ -287,7 +313,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  	unsigned long isolated = 0;
>  
>  restart:
> -	l = lock_list_lru_of_memcg(lru, nid, memcg, irq_off, true);
> +	l = lock_list_lru_of_memcg(lru, nid, memcg, irq_off, NULL, true);
>  	if (!l)
>  		return isolated;
>  	list_for_each_safe(item, n, &l->list) {
> @@ -328,7 +354,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  			BUG();
>  		}
>  	}
> -	unlock_list_lru(l, irq_off);
> +	unlock_list_lru(l, irq_off, NULL);
>  out:
>  	return isolated;
>  }
> @@ -510,17 +536,14 @@ static inline bool memcg_list_lru_allocated(struct mem_cgroup *memcg,
>  	return idx < 0 || xa_load(&lru->xa, idx);
>  }
>  
> -int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
> -			 gfp_t gfp)
> +static int __memcg_list_lru_alloc(struct mem_cgroup *memcg,
> +				  struct list_lru *lru, gfp_t gfp)
>  {
>  	unsigned long flags;
>  	struct list_lru_memcg *mlru = NULL;
>  	struct mem_cgroup *pos, *parent;
>  	XA_STATE(xas, &lru->xa, 0);
>  
> -	if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
> -		return 0;
> -
>  	gfp &= GFP_RECLAIM_MASK;
>  	/*
>  	 * Because the list_lru can be reparented to the parent cgroup's
> @@ -561,6 +584,38 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
>  
>  	return xas_error(&xas);
>  }
> +
> +int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
> +			 gfp_t gfp)
> +{
> +	if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
> +		return 0;
> +
> +	return __memcg_list_lru_alloc(memcg, lru, gfp);
> +}
> +
> +int memcg_list_lru_alloc_folio(struct folio *folio, struct list_lru *lru,
> +			       gfp_t gfp)
> +{
> +	struct mem_cgroup *memcg;
> +	int res;
> +
> +	if (!list_lru_memcg_aware(lru))
> +		return 0;
> +
> +	/* Fast path when list_lru heads already exist */
> +	rcu_read_lock();
> +	res = memcg_list_lru_allocated(folio_memcg(folio), lru);
> +	rcu_read_unlock();
> +	if (likely(res))
> +		return 0;
> +
> +	/* Need to allocate, pin the memcg */
> +	memcg = get_mem_cgroup_from_folio(folio);
> +	res = __memcg_list_lru_alloc(memcg, lru, gfp);
> +	mem_cgroup_put(memcg);
> +	return res;
> +}
>  #else
>  static inline void memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
>  {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a47fb68dd65f..f381cb6bdff1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4015,11 +4015,6 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
>  	for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++)
>  		memcg->cgwb_frn[i].done =
>  			__WB_COMPLETION_INIT(&memcg_cgwb_frn_waitq);
> -#endif
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	spin_lock_init(&memcg->deferred_split_queue.split_queue_lock);
> -	INIT_LIST_HEAD(&memcg->deferred_split_queue.split_queue);
> -	memcg->deferred_split_queue.split_queue_len = 0;
>  #endif
>  	lru_gen_init_memcg(memcg);
>  	return memcg;
> @@ -4167,11 +4162,10 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
>  	zswap_memcg_offline_cleanup(memcg);
>  
>  	memcg_offline_kmem(memcg);
> -	reparent_deferred_split_queue(memcg);
>  	/*
> -	 * The reparenting of objcg must be after the reparenting of the
> -	 * list_lru and deferred_split_queue above, which ensures that they will
> -	 * not mistakenly get the parent list_lru and deferred_split_queue.
> +	 * The reparenting of objcg must be after the reparenting of
> +	 * the list_lru in memcg_offline_kmem(), which ensures that
> +	 * they will not mistakenly get the parent list_lru.
>  	 */
>  	memcg_reparent_objcgs(memcg);
>  	reparent_shrinker_deferred(memcg);
> diff --git a/mm/memory.c b/mm/memory.c
> index 38062f8e1165..4dad1a7890aa 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4651,13 +4651,19 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
>  	while (orders) {
>  		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
>  		folio = vma_alloc_folio(gfp, order, vma, addr);
> -		if (folio) {
> -			if (!mem_cgroup_swapin_charge_folio(folio, vma->vm_mm,
> -							    gfp, entry))
> -				return folio;
> +		if (!folio)
> +			goto next;
> +		if (mem_cgroup_swapin_charge_folio(folio, vma->vm_mm, gfp, entry)) {
>  			count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK_CHARGE);
>  			folio_put(folio);
> +			goto next;
>  		}
> +		if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
> +			folio_put(folio);
> +			goto fallback;
> +		}
> +		return folio;
> +next:
>  		count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
>  		order = next_order(&orders, order);
>  	}
> @@ -5168,24 +5174,28 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
>  	while (orders) {
>  		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
>  		folio = vma_alloc_folio(gfp, order, vma, addr);
> -		if (folio) {
> -			if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
> -				count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> -				folio_put(folio);
> -				goto next;
> -			}
> -			folio_throttle_swaprate(folio, gfp);
> -			/*
> -			 * When a folio is not zeroed during allocation
> -			 * (__GFP_ZERO not used) or user folios require special
> -			 * handling, folio_zero_user() is used to make sure
> -			 * that the page corresponding to the faulting address
> -			 * will be hot in the cache after zeroing.
> -			 */
> -			if (user_alloc_needs_zeroing())
> -				folio_zero_user(folio, vmf->address);
> -			return folio;
> +		if (!folio)
> +			goto next;
> +		if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
> +			count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> +			folio_put(folio);
> +			goto next;
>  		}
> +		if (memcg_list_lru_alloc_folio(folio, &deferred_split_lru, gfp)) {
> +			folio_put(folio);
> +			goto fallback;
> +		}
> +		folio_throttle_swaprate(folio, gfp);
> +		/*
> +		 * When a folio is not zeroed during allocation
> +		 * (__GFP_ZERO not used) or user folios require special
> +		 * handling, folio_zero_user() is used to make sure
> +		 * that the page corresponding to the faulting address
> +		 * will be hot in the cache after zeroing.
> +		 */
> +		if (user_alloc_needs_zeroing())
> +			folio_zero_user(folio, vmf->address);
> +		return folio;
>  next:
>  		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
>  		order = next_order(&orders, order);
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index cec7bb758bdd..ed357e73b7e9 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1388,19 +1388,6 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
>  	pr_debug("On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
>  }
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -static void pgdat_init_split_queue(struct pglist_data *pgdat)
> -{
> -	struct deferred_split *ds_queue = &pgdat->deferred_split_queue;
> -
> -	spin_lock_init(&ds_queue->split_queue_lock);
> -	INIT_LIST_HEAD(&ds_queue->split_queue);
> -	ds_queue->split_queue_len = 0;
> -}
> -#else
> -static void pgdat_init_split_queue(struct pglist_data *pgdat) {}
> -#endif
> -
>  #ifdef CONFIG_COMPACTION
>  static void pgdat_init_kcompactd(struct pglist_data *pgdat)
>  {
> @@ -1417,7 +1404,6 @@ static void __meminit pgdat_init_internals(struct pglist_data *pgdat)
>  	pgdat_resize_init(pgdat);
>  	pgdat_kswapd_lock_init(pgdat);
>  
> -	pgdat_init_split_queue(pgdat);
>  	pgdat_init_kcompactd(pgdat);
>  
>  	init_waitqueue_head(&pgdat->kswapd_wait);
> -- 
> 2.53.0
> 

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[David Hildenbrand (Arm)]

On 3/11/26 16:46, Johannes Weiner wrote:
> Fixing David's email address. Sorry! Full quote below.
>

I still catch everything sent to the old address as long as a mailing
list I am subscribed to is CCed :)

-- 
Cheers,

David

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Usama Arif]

On 11/03/2026 18:43, Johannes Weiner wrote:
> The deferred split queue handles cgroups in a suboptimal fashion. The
> queue is per-NUMA node or per-cgroup, not the intersection. That means
> on a cgrouped system, a node-restricted allocation entering reclaim
> can end up splitting large pages on other nodes:
> 
> 	alloc/unmap
> 	  deferred_split_folio()
> 	    list_add_tail(memcg->split_queue)
> 	    set_shrinker_bit(memcg, node, deferred_shrinker_id)
> 
> 	for_each_zone_zonelist_nodemask(restricted_nodes)
> 	  mem_cgroup_iter()
> 	    shrink_slab(node, memcg)
> 	      shrink_slab_memcg(node, memcg)
> 	        if test_shrinker_bit(memcg, node, deferred_shrinker_id)
> 	          deferred_split_scan()
> 	            walks memcg->split_queue
> 
> The shrinker bit adds an imperfect guard rail. As soon as the cgroup
> has a single large page on the node of interest, all large pages owned
> by that memcg, including those on other nodes, will be split.
> 
> list_lru properly sets up per-node, per-cgroup lists. As a bonus, it
> streamlines a lot of the list operations and reclaim walks. It's used
> widely by other major shrinkers already. Convert the deferred split
> queue as well.
> 
> The list_lru per-memcg heads are instantiated on demand when the first
> object of interest is allocated for a cgroup, by calling
> memcg_list_lru_alloc(). Add calls to where splittable pages are
> created: anon faults, swapin faults, khugepaged collapse.
> 
> These calls create all possible node heads for the cgroup at once, so
> the migration code (between nodes) doesn't need any special care.
> 
> The folio_test_partially_mapped() state is currently protected and
> serialized wrt LRU state by the deferred split queue lock. To
> facilitate the transition, add helpers to the list_lru API to allow
> caller-side locking.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/huge_mm.h    |   6 +-
>  include/linux/list_lru.h   |  48 ++++++
>  include/linux/memcontrol.h |   4 -
>  include/linux/mmzone.h     |  12 --
>  mm/huge_memory.c           | 326 +++++++++++--------------------------
>  mm/internal.h              |   2 +-
>  mm/khugepaged.c            |   7 +
>  mm/list_lru.c              | 197 ++++++++++++++--------
>  mm/memcontrol.c            |  12 +-
>  mm/memory.c                |  52 +++---
>  mm/mm_init.c               |  14 --
>  11 files changed, 310 insertions(+), 370 deletions(-)
> 

[..]

> @@ -3802,33 +3706,25 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>  	struct folio *new_folio, *next;
>  	int old_order = folio_order(folio);
>  	int ret = 0;
> -	struct deferred_split *ds_queue;
> +	struct list_lru_one *l;
>  
>  	VM_WARN_ON_ONCE(!mapping && end);
>  	/* Prevent deferred_split_scan() touching ->_refcount */
> -	ds_queue = folio_split_queue_lock(folio);
> +	l = list_lru_lock(&deferred_split_lru, folio_nid(folio), folio_memcg(folio));

Hello Johannes!

I think we need folio_memcg() to be under rcu_read_lock()? 
folio_memcg() calls obj_cgroup_memcg() which has lockdep_assert_once(rcu_read_lock_held()).

folio_split_queue_lock() wraps split_queue_lock() under rcu_read_lock() so wasnt an issue.
 

>  	if (folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
>  		struct swap_cluster_info *ci = NULL;
>  		struct lruvec *lruvec;
>  
>  		if (old_order > 1) {
> -			if (!list_empty(&folio->_deferred_list)) {
> -				ds_queue->split_queue_len--;
> -				/*
> -				 * Reinitialize page_deferred_list after removing the
> -				 * page from the split_queue, otherwise a subsequent
> -				 * split will see list corruption when checking the
> -				 * page_deferred_list.
> -				 */
> -				list_del_init(&folio->_deferred_list);
> -			}
> +			__list_lru_del(&deferred_split_lru, l,
> +				       &folio->_deferred_list, folio_nid(folio));
>  			if (folio_test_partially_mapped(folio)) {
>  				folio_clear_partially_mapped(folio);
>  				mod_mthp_stat(old_order,
>  					MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
>  			}
>  		}
> -		split_queue_unlock(ds_queue);
> +		list_lru_unlock(l);
>  		if (mapping) {
>  			int nr = folio_nr_pages(folio);
>  
> @@ -3929,7 +3825,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>  		if (ci)
>  			swap_cluster_unlock(ci);
>  	} else {
> -		split_queue_unlock(ds_queue);
> +		list_lru_unlock(l);
>  		return -EAGAIN;
>  	}
>  
[..]

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Johannes Weiner]

On Wed, Mar 11, 2026 at 08:00:29PM +0300, Usama Arif wrote:
> On 11/03/2026 18:43, Johannes Weiner wrote:
> > @@ -3802,33 +3706,25 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
> >  	struct folio *new_folio, *next;
> >  	int old_order = folio_order(folio);
> >  	int ret = 0;
> > -	struct deferred_split *ds_queue;
> > +	struct list_lru_one *l;
> >  
> >  	VM_WARN_ON_ONCE(!mapping && end);
> >  	/* Prevent deferred_split_scan() touching ->_refcount */
> > -	ds_queue = folio_split_queue_lock(folio);
> > +	l = list_lru_lock(&deferred_split_lru, folio_nid(folio), folio_memcg(folio));
> 
> Hello Johannes!
> 
> I think we need folio_memcg() to be under rcu_read_lock()? 
> folio_memcg() calls obj_cgroup_memcg() which has lockdep_assert_once(rcu_read_lock_held()).
> 
> folio_split_queue_lock() wraps split_queue_lock() under rcu_read_lock() so wasnt an issue.

In this case, the caller has interrupts disabled, which implies an RCU
read-side critical section.

That's also why it's using the plain list_lru_lock(), not the irq
variant. Same for the lruvec lock a few lines down. I followed the
example of none of that being documented, either ;)

How do folks feel about a VM_WARN_ON(!irqs_disabled()) at the top?

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Johannes Weiner]

On Wed, Mar 11, 2026 at 01:42:32PM -0400, Johannes Weiner wrote:
> On Wed, Mar 11, 2026 at 08:00:29PM +0300, Usama Arif wrote:
> > On 11/03/2026 18:43, Johannes Weiner wrote:
> > > @@ -3802,33 +3706,25 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
> > >  	struct folio *new_folio, *next;
> > >  	int old_order = folio_order(folio);
> > >  	int ret = 0;
> > > -	struct deferred_split *ds_queue;
> > > +	struct list_lru_one *l;
> > >  
> > >  	VM_WARN_ON_ONCE(!mapping && end);
> > >  	/* Prevent deferred_split_scan() touching ->_refcount */
> > > -	ds_queue = folio_split_queue_lock(folio);
> > > +	l = list_lru_lock(&deferred_split_lru, folio_nid(folio), folio_memcg(folio));
> > 
> > Hello Johannes!
> > 
> > I think we need folio_memcg() to be under rcu_read_lock()? 
> > folio_memcg() calls obj_cgroup_memcg() which has lockdep_assert_once(rcu_read_lock_held()).
> > 
> > folio_split_queue_lock() wraps split_queue_lock() under rcu_read_lock() so wasnt an issue.
> 
> In this case, the caller has interrupts disabled, which implies an RCU
> read-side critical section.
> 
> That's also why it's using the plain list_lru_lock(), not the irq
> variant. Same for the lruvec lock a few lines down. I followed the
> example of none of that being documented, either ;)
> 
> How do folks feel about a VM_WARN_ON(!irqs_disabled()) at the top?

Okay, lockdep actually does warn. rcu_read_lock_held() is explicit and
not appeased by implicit RCU sections.

Paul pointed me to rcu_read_lock_any_held(), which we could use in
obj_cgroup_memcg() to suppress the splat and permit implicit RCU.

Or we can make rcu_read_lock() explicit in the above code.

Any preferences for how we want to handle this in MM code?

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Shakeel Butt]

On Wed, Mar 11, 2026 at 03:24:18PM -0400, Johannes Weiner wrote:
> On Wed, Mar 11, 2026 at 01:42:32PM -0400, Johannes Weiner wrote:
> > On Wed, Mar 11, 2026 at 08:00:29PM +0300, Usama Arif wrote:
> > > On 11/03/2026 18:43, Johannes Weiner wrote:
> > > > @@ -3802,33 +3706,25 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
> > > >  	struct folio *new_folio, *next;
> > > >  	int old_order = folio_order(folio);
> > > >  	int ret = 0;
> > > > -	struct deferred_split *ds_queue;
> > > > +	struct list_lru_one *l;
> > > >  
> > > >  	VM_WARN_ON_ONCE(!mapping && end);
> > > >  	/* Prevent deferred_split_scan() touching ->_refcount */
> > > > -	ds_queue = folio_split_queue_lock(folio);
> > > > +	l = list_lru_lock(&deferred_split_lru, folio_nid(folio), folio_memcg(folio));
> > > 
> > > Hello Johannes!
> > > 
> > > I think we need folio_memcg() to be under rcu_read_lock()? 
> > > folio_memcg() calls obj_cgroup_memcg() which has lockdep_assert_once(rcu_read_lock_held()).
> > > 
> > > folio_split_queue_lock() wraps split_queue_lock() under rcu_read_lock() so wasnt an issue.
> > 
> > In this case, the caller has interrupts disabled, which implies an RCU
> > read-side critical section.
> > 
> > That's also why it's using the plain list_lru_lock(), not the irq
> > variant. Same for the lruvec lock a few lines down. I followed the
> > example of none of that being documented, either ;)
> > 
> > How do folks feel about a VM_WARN_ON(!irqs_disabled()) at the top?
> 
> Okay, lockdep actually does warn. rcu_read_lock_held() is explicit and
> not appeased by implicit RCU sections.
> 
> Paul pointed me to rcu_read_lock_any_held(), which we could use in
> obj_cgroup_memcg() to suppress the splat and permit implicit RCU.
> 
> Or we can make rcu_read_lock() explicit in the above code.
> 
> Any preferences for how we want to handle this in MM code?

I would vote for explicit rcu_read_lock() to be consistent with other places.

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Yosry Ahmed]

> > Okay, lockdep actually does warn. rcu_read_lock_held() is explicit and
> > not appeased by implicit RCU sections.
> >
> > Paul pointed me to rcu_read_lock_any_held(), which we could use in
> > obj_cgroup_memcg() to suppress the splat and permit implicit RCU.
> >
> > Or we can make rcu_read_lock() explicit in the above code.
> >
> > Any preferences for how we want to handle this in MM code?
>
> I would vote for explicit rcu_read_lock() to be consistent with other places.

+1

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Dave Chinner]

On Wed, Mar 11, 2026 at 11:43:58AM -0400, Johannes Weiner wrote:
> The deferred split queue handles cgroups in a suboptimal fashion. The
> queue is per-NUMA node or per-cgroup, not the intersection. That means
> on a cgrouped system, a node-restricted allocation entering reclaim
> can end up splitting large pages on other nodes:
> 
> 	alloc/unmap
> 	  deferred_split_folio()
> 	    list_add_tail(memcg->split_queue)
> 	    set_shrinker_bit(memcg, node, deferred_shrinker_id)
> 
> 	for_each_zone_zonelist_nodemask(restricted_nodes)
> 	  mem_cgroup_iter()
> 	    shrink_slab(node, memcg)
> 	      shrink_slab_memcg(node, memcg)
> 	        if test_shrinker_bit(memcg, node, deferred_shrinker_id)
> 	          deferred_split_scan()
> 	            walks memcg->split_queue
> 
> The shrinker bit adds an imperfect guard rail. As soon as the cgroup
> has a single large page on the node of interest, all large pages owned
> by that memcg, including those on other nodes, will be split.
> 
> list_lru properly sets up per-node, per-cgroup lists. As a bonus, it
> streamlines a lot of the list operations and reclaim walks. It's used
> widely by other major shrinkers already. Convert the deferred split
> queue as well.
> 
> The list_lru per-memcg heads are instantiated on demand when the first
> object of interest is allocated for a cgroup, by calling
> memcg_list_lru_alloc(). Add calls to where splittable pages are
> created: anon faults, swapin faults, khugepaged collapse.
> 
> These calls create all possible node heads for the cgroup at once, so
> the migration code (between nodes) doesn't need any special care.
> 
> The folio_test_partially_mapped() state is currently protected and
> serialized wrt LRU state by the deferred split queue lock. To
> facilitate the transition, add helpers to the list_lru API to allow
> caller-side locking.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/huge_mm.h    |   6 +-
>  include/linux/list_lru.h   |  48 ++++++
>  include/linux/memcontrol.h |   4 -
>  include/linux/mmzone.h     |  12 --
>  mm/huge_memory.c           | 326 +++++++++++--------------------------
>  mm/internal.h              |   2 +-
>  mm/khugepaged.c            |   7 +
>  mm/list_lru.c              | 197 ++++++++++++++--------
>  mm/memcontrol.c            |  12 +-
>  mm/memory.c                |  52 +++---
>  mm/mm_init.c               |  14 --
>  11 files changed, 310 insertions(+), 370 deletions(-)

Can you please split this up into multiple patches (i.e. one logical
change per patch) to make it easier to review?

i.e. just from the list-lru persepective, there's multiple complex
changes in the series - locking API changes, new locking primitives,
internally locked functions exposed to callers allowing external
locking, etc. These need to be looked at individually and in
isolation so we can actually discuss the finer details, and that's
almost impossible to do when they are all smashed into one massive
patch.

-Dave.
-- 
Dave Chinner
dgc@kernel.org

[syzbot ci] Re: mm: switch deferred split shrinker to list_lru

[syzbot ci]

syzbot ci has tested the following series

[v1] mm: switch deferred split shrinker to list_lru
https://lore.kernel.org/all/20260311154358.150977-1-hannes@cmpxchg.org
* [PATCH] mm: switch deferred split shrinker to list_lru

and found the following issue:
WARNING in folio_memcg

Full report is available here:
https://ci.syzbot.org/series/3cf5ecdb-21ef-4894-a22d-6eb1eb437395

***

WARNING in folio_memcg

tree:      mm-new
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base:      f543926f9d0c3f6dfb354adfe7fbaeedd1277c6b
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/6c96ae71-4f8b-4153-8306-440a79f2b2e8/config
C repro:   https://ci.syzbot.org/findings/25285d24-81d9-42b6-b715-1749d43db688/c_repro
syz repro: https://ci.syzbot.org/findings/25285d24-81d9-42b6-b715-1749d43db688/syz_repro

------------[ cut here ]------------
debug_locks && !(rcu_read_lock_held() || lock_is_held(&(&cgroup_mutex)->dep_map))
WARNING: ./include/linux/memcontrol.h:376 at obj_cgroup_memcg include/linux/memcontrol.h:376 [inline], CPU#1: syz.0.17/5956
WARNING: ./include/linux/memcontrol.h:376 at folio_memcg+0x148/0x1c0 include/linux/memcontrol.h:430, CPU#1: syz.0.17/5956
Modules linked in:
CPU: 1 UID: 0 PID: 5956 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:obj_cgroup_memcg include/linux/memcontrol.h:376 [inline]
RIP: 0010:folio_memcg+0x148/0x1c0 include/linux/memcontrol.h:430
Code: 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 8f 59 fb ff 48 8b 03 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc e8 b9 39 92 ff 90 <0f> 0b 90 eb ca 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c ef fe ff ff
RSP: 0018:ffffc90005d86b98 EFLAGS: 00010093
RAX: ffffffff823359c7 RBX: ffff8881749d1080 RCX: ffff88817250d7c0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffea00068f8007 R09: 1ffffd4000d1f000
R10: dffffc0000000000 R11: fffff94000d1f001 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffffea00068f8000 R15: ffffea00068f8030
FS:  0000555584c04500(0000) GS:ffff8882a9466000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2e563fff CR3: 0000000175ed0000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 __folio_freeze_and_split_unmapped+0x1db/0x31f0 mm/huge_memory.c:3766
 __folio_split+0xa99/0x1570 mm/huge_memory.c:4029
 madvise_cold_or_pageout_pte_range+0xe3b/0x2220 mm/madvise.c:501
 walk_pmd_range mm/pagewalk.c:129 [inline]
 walk_pud_range mm/pagewalk.c:223 [inline]
 walk_p4d_range mm/pagewalk.c:261 [inline]
 walk_pgd_range+0x1032/0x1d30 mm/pagewalk.c:302
 __walk_page_range+0x14c/0x710 mm/pagewalk.c:410
 walk_page_range_vma_unsafe+0x309/0x410 mm/pagewalk.c:714
 madvise_pageout_page_range mm/madvise.c:620 [inline]
 madvise_pageout mm/madvise.c:645 [inline]
 madvise_vma_behavior+0x2883/0x44d0 mm/madvise.c:1356
 madvise_walk_vmas+0x573/0xae0 mm/madvise.c:1711
 madvise_do_behavior+0x386/0x540 mm/madvise.c:1927
 do_madvise+0x1fa/0x2e0 mm/madvise.c:2020
 __do_sys_madvise mm/madvise.c:2029 [inline]
 __se_sys_madvise mm/madvise.c:2027 [inline]
 __x64_sys_madvise+0xa6/0xc0 mm/madvise.c:2027
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb99159c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc93688748 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007fb991815fa0 RCX: 00007fb99159c799
RDX: 0000000000000015 RSI: 0000000000002000 RDI: 0000200000f0f000
RBP: 00007fb991632bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb991815fac R14: 00007fb991815fa0 R15: 00007fb991815fa0
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.

Re: [PATCH] mm: switch deferred split shrinker to list_lru

[Johannes Weiner]

On Thu, Mar 12, 2026 at 09:23:35AM +1100, Dave Chinner wrote:
> On Wed, Mar 11, 2026 at 11:43:58AM -0400, Johannes Weiner wrote:
> > The deferred split queue handles cgroups in a suboptimal fashion. The
> > queue is per-NUMA node or per-cgroup, not the intersection. That means
> > on a cgrouped system, a node-restricted allocation entering reclaim
> > can end up splitting large pages on other nodes:
> > 
> > 	alloc/unmap
> > 	  deferred_split_folio()
> > 	    list_add_tail(memcg->split_queue)
> > 	    set_shrinker_bit(memcg, node, deferred_shrinker_id)
> > 
> > 	for_each_zone_zonelist_nodemask(restricted_nodes)
> > 	  mem_cgroup_iter()
> > 	    shrink_slab(node, memcg)
> > 	      shrink_slab_memcg(node, memcg)
> > 	        if test_shrinker_bit(memcg, node, deferred_shrinker_id)
> > 	          deferred_split_scan()
> > 	            walks memcg->split_queue
> > 
> > The shrinker bit adds an imperfect guard rail. As soon as the cgroup
> > has a single large page on the node of interest, all large pages owned
> > by that memcg, including those on other nodes, will be split.
> > 
> > list_lru properly sets up per-node, per-cgroup lists. As a bonus, it
> > streamlines a lot of the list operations and reclaim walks. It's used
> > widely by other major shrinkers already. Convert the deferred split
> > queue as well.
> > 
> > The list_lru per-memcg heads are instantiated on demand when the first
> > object of interest is allocated for a cgroup, by calling
> > memcg_list_lru_alloc(). Add calls to where splittable pages are
> > created: anon faults, swapin faults, khugepaged collapse.
> > 
> > These calls create all possible node heads for the cgroup at once, so
> > the migration code (between nodes) doesn't need any special care.
> > 
> > The folio_test_partially_mapped() state is currently protected and
> > serialized wrt LRU state by the deferred split queue lock. To
> > facilitate the transition, add helpers to the list_lru API to allow
> > caller-side locking.
> > 
> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> > ---
> >  include/linux/huge_mm.h    |   6 +-
> >  include/linux/list_lru.h   |  48 ++++++
> >  include/linux/memcontrol.h |   4 -
> >  include/linux/mmzone.h     |  12 --
> >  mm/huge_memory.c           | 326 +++++++++++--------------------------
> >  mm/internal.h              |   2 +-
> >  mm/khugepaged.c            |   7 +
> >  mm/list_lru.c              | 197 ++++++++++++++--------
> >  mm/memcontrol.c            |  12 +-
> >  mm/memory.c                |  52 +++---
> >  mm/mm_init.c               |  14 --
> >  11 files changed, 310 insertions(+), 370 deletions(-)
> 
> Can you please split this up into multiple patches (i.e. one logical
> change per patch) to make it easier to review?

No problem, I'll do that and send out a v2.

The list_lru changes started as only the locking functions, then
things kept creeping in...

Thanks