[PATCH v4 0/8] mm: switch THP shrinker to list_lru

[PATCH v4 0/8] mm: switch THP shrinker to list_lru

[Johannes Weiner]

This is version 4 of switching the THP shrinker to list_lru.

Changes in v4:
- guard folio_memcg_alloc_deferred() with mem_cgroup_disabled() to fix
  NULL deref in __memcg_list_lru_alloc() when booting with
  cgroup_disable=memory (e.g., kdump capture kernel) -- reported and
  tested by Mikhail Zaslonko on s390 and x86
- flatten if (folio) branches in alloc_swap_folio() and alloc_anon_folio()
  in a prep patch so the list_lru allocation additions are a clean minimal
  diff (Lorenzo)
- folio_memcg_alloc_deferred() moved out of alloc_charge_folio() into the
  anon-only collapse_huge_page() path; collapse_file() shares that helper
  but its pages don't go on the THP shrinker queue (David)
- guard folio_memcg_alloc_deferred() with order > 1; mTHPs below order-2
  can't be queued on the deferred split list (David)
- make deferred_split_lru static, hide behind folio_memcg_alloc_deferred()
  wrapper with GFP_KERNEL (Lorenzo)
- rename l -> lru throughout huge_memory.c (Lorenzo)
- kdoc for folio_memcg_list_lru_alloc() (Lorenzo)
- list_lru_lock_irq()/unlock_irq()/add_irq() irq-disabling variants;
  use list_lru_add_irq() in deferred_split_scan() (Lorenzo)
- reorder shrinker_free() before list_lru_destroy() (Lorenzo)

Changes in v3:
- dedicated lockdep_key for irqsafe deferred_split_lru.lock (syzbot)
- conditional list_lru ops in __folio_freeze_and_split_unmapped() (syzbot)
- annotate runs of inscrutable false, NULL, false function arguments (David)
- rename to folio_memcg_list_lru_alloc() (David)

Changes in v2:
- explicit rcu_read_lock() in __folio_freeze_and_split_unmapped() (Usama)
- split out list_lru prep bits (Dave)

The open-coded deferred split queue has issues. It's not NUMA-aware
(when cgroup is enabled), and it's more complicated in the callsites
interacting with it. Switching to list_lru fixes the NUMA problem and
streamlines things. It also simplifies planned shrinker work.

Patches 1-4 are cleanups and small refactors in list_lru code. They're
basically independent, but make the THP shrinker conversion easier.

Patch 5 extends the list_lru API to allow the caller to control the
locking scope. The THP shrinker has private state it needs to keep
synchronized with the LRU state.

Patch 6 extends the list_lru API with a convenience helper to do
list_lru head allocation (memcg_list_lru_alloc) when coming from a
folio. Anon THPs are instantiated in several places, and with the
folio reparenting patches pending, folio_memcg() access is now a more
delicate dance. This avoids having to replicate that dance everywhere.

Patch 7 flattens the folio allocation retry loops in alloc_swap_folio()
and alloc_anon_folio() without functional change, in preparation for
patch 8.

Patch 8 finally switches the deferred_split_queue to list_lru.

Based on mm-unstable.

 include/linux/huge_mm.h    |   7 +-
 include/linux/list_lru.h   |  68 +++++++++
 include/linux/memcontrol.h |   4 -
 include/linux/mmzone.h     |  12 --
 mm/huge_memory.c           | 355 ++++++++++++++-----------------------------
 mm/internal.h              |   2 +-
 mm/khugepaged.c            |   3 +
 mm/list_lru.c              | 220 ++++++++++++++++++---------
 mm/memcontrol.c            |  12 +-
 mm/memory.c                |  52 ++++---
 mm/mm_init.c               |  15 --
 11 files changed, 374 insertions(+), 376 deletions(-)

[PATCH v4 1/8] mm: list_lru: lock_list_lru_of_memcg() cannot return NULL if !skip_empty

[Johannes Weiner]

skip_empty is only for the shrinker to abort and skip a list that's
empty or whose cgroup is being deleted.

For list additions and deletions, the cgroup hierarchy is walked
upwards until a valid list_lru head is found, or it will fall back to
the node list. Acquiring the lock won't fail. Remove the NULL checks
in those callers.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/list_lru.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index dd29bcf8eb5f..d3619961a7ac 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -165,8 +165,6 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
 	struct list_lru_one *l;
 
 	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
-	if (!l)
-		return false;
 	if (list_empty(item)) {
 		list_add_tail(item, &l->list);
 		/* Set shrinker bit if the first element was added */
@@ -204,9 +202,8 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
 {
 	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l;
+
 	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
-	if (!l)
-		return false;
 	if (!list_empty(item)) {
 		list_del_init(item);
 		l->nr_items--;
-- 
2.54.0

[PATCH v4 2/8] mm: list_lru: deduplicate unlock_list_lru()

[Johannes Weiner]

The MEMCG and !MEMCG variants are the same. lock_list_lru() has the
same pattern when bailing. Consolidate into a common implementation.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/list_lru.c | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index d3619961a7ac..9a68177619bf 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -15,6 +15,14 @@
 #include "slab.h"
 #include "internal.h"
 
+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);
+}
+
 #ifdef CONFIG_MEMCG
 static LIST_HEAD(memcg_list_lrus);
 static DEFINE_MUTEX(list_lrus_mutex);
@@ -67,10 +75,7 @@ static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
 	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);
+		unlock_list_lru(l, irq);
 		return false;
 	}
 	return true;
@@ -101,14 +106,6 @@ 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)
 {
@@ -147,14 +144,6 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 
 	return l;
 }
-
-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);
-}
 #endif /* CONFIG_MEMCG */
 
 /* The caller must ensure the memcg lifetime. */
-- 
2.54.0

[PATCH v4 3/8] mm: list_lru: move list dead check to lock_list_lru_of_memcg()

[Johannes Weiner]

Only the MEMCG variant of lock_list_lru() needs to check if there is a
race with cgroup deletion and list reparenting. Move the check to the
caller, so that the next patch can unify the lock_list_lru() variants.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/list_lru.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 9a68177619bf..9da6fce19832 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -68,17 +68,12 @@ 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)
+static inline void 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)) {
-		unlock_list_lru(l, irq);
-		return false;
-	}
-	return true;
 }
 
 static inline struct list_lru_one *
@@ -90,9 +85,13 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 	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);
+		if (likely(READ_ONCE(l->nr_items) != LONG_MIN)) {
+			rcu_read_unlock();
+			return l;
+		}
+		unlock_list_lru(l, irq);
 	}
 	/*
 	 * Caller may simply bail out if raced with reparenting or
-- 
2.54.0

[PATCH v4 4/8] mm: list_lru: deduplicate lock_list_lru()

[Johannes Weiner]

The MEMCG and !MEMCG paths have the same pattern. Share the code.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/list_lru.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 9da6fce19832..65962dbf6dda 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -15,6 +15,14 @@
 #include "slab.h"
 #include "internal.h"
 
+static inline void lock_list_lru(struct list_lru_one *l, bool irq)
+{
+	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_off)
 {
 	if (irq_off)
@@ -68,14 +76,6 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
 	return &lru->node[nid].lru;
 }
 
-static inline void lock_list_lru(struct list_lru_one *l, bool irq)
-{
-	if (irq)
-		spin_lock_irq(&l->lock);
-	else
-		spin_lock(&l->lock);
-}
-
 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)
@@ -136,10 +136,7 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 {
 	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);
 
 	return l;
 }
-- 
2.54.0

[PATCH v4 5/8] mm: list_lru: introduce caller locking for additions and deletions

[Johannes Weiner]

Locking is currently internal to the list_lru API. However, a caller
might want to keep auxiliary state synchronized with the LRU state.

For example, the THP shrinker uses the lock of its custom LRU to keep
PG_partially_mapped and vmstats consistent.

To allow the THP shrinker to switch to list_lru, provide normal and
irqsafe locking primitives as well as caller-locked variants of the
addition and deletion functions.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/list_lru.h |  41 ++++++++++++
 mm/list_lru.c            | 131 ++++++++++++++++++++++++++++++---------
 2 files changed, 141 insertions(+), 31 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index fe739d35a864..c79ed378311f 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -83,6 +83,44 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
 			 gfp_t gfp);
 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_irq(struct list_lru *lru, int nid,
+		struct mem_cgroup *memcg);
+void list_lru_unlock_irq(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
@@ -115,6 +153,9 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
 bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
 		    struct mem_cgroup *memcg);
 
+bool list_lru_add_irq(struct list_lru *lru, struct list_head *item, int nid,
+		      struct mem_cgroup *memcg);
+
 /**
  * list_lru_add_obj: add an element to the lru list's tail
  * @lru: the lru pointer
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 65962dbf6dda..df58226eea8c 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -15,17 +15,23 @@
 #include "slab.h"
 #include "internal.h"
 
-static inline void lock_list_lru(struct list_lru_one *l, bool irq)
+static inline void lock_list_lru(struct list_lru_one *l, bool irq,
+				 unsigned long *irq_flags)
 {
-	if (irq)
+	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_off)
+static inline void unlock_list_lru(struct list_lru_one *l, bool irq_off,
+				   unsigned long *irq_flags)
 {
-	if (irq_off)
+	if (irq_flags)
+		spin_unlock_irqrestore(&l->lock, *irq_flags);
+	else if (irq_off)
 		spin_unlock_irq(&l->lock);
 	else
 		spin_unlock(&l->lock);
@@ -78,7 +84,7 @@ 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;
 
@@ -86,12 +92,12 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 again:
 	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
 	if (likely(l)) {
-		lock_list_lru(l, irq);
+		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);
+		unlock_list_lru(l, irq, irq_flags);
 	}
 	/*
 	 * Caller may simply bail out if raced with reparenting or
@@ -132,38 +138,106 @@ 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;
 
-	lock_list_lru(l, irq);
+	lock_list_lru(l, irq, irq_flags);
 
 	return l;
 }
 #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_one *list_lru_lock(struct list_lru *lru, int nid,
+				   struct mem_cgroup *memcg)
 {
-	struct list_lru_node *nlru = &lru->node[nid];
-	struct list_lru_one *l;
+	return lock_list_lru_of_memcg(lru, nid, memcg, /*irq=*/false,
+				      /*irq_flags=*/NULL, /*skip_empty=*/false);
+}
+
+void list_lru_unlock(struct list_lru_one *l)
+{
+	unlock_list_lru(l, /*irq_off=*/false, /*irq_flags=*/NULL);
+}
+
+struct list_lru_one *list_lru_lock_irq(struct list_lru *lru, int nid,
+				       struct mem_cgroup *memcg)
+{
+	return lock_list_lru_of_memcg(lru, nid, memcg, /*irq=*/true,
+				      /*irq_flags=*/NULL, /*skip_empty=*/false);
+}
+
+void list_lru_unlock_irq(struct list_lru_one *l)
+{
+	unlock_list_lru(l, /*irq_off=*/true, /*irq_flags=*/NULL);
+}
 
-	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
+struct list_lru_one *list_lru_lock_irqsave(struct list_lru *lru, int nid,
+					   struct mem_cgroup *memcg,
+					   unsigned long *flags)
+{
+	return lock_list_lru_of_memcg(lru, nid, memcg, /*irq=*/true,
+				      /*irq_flags=*/flags, /*skip_empty=*/false);
+}
+
+void list_lru_unlock_irqrestore(struct list_lru_one *l, unsigned long *flags)
+{
+	unlock_list_lru(l, /*irq_off=*/true, /*irq_flags=*/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)) {
 		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);
+		atomic_long_inc(&lru->node[nid].nr_items);
 		return true;
 	}
-	unlock_list_lru(l, false);
 	return false;
 }
 EXPORT_SYMBOL_GPL(list_lru_add);
 
+bool __list_lru_del(struct list_lru *lru, struct list_lru_one *l,
+		    struct list_head *item, int nid)
+{
+	if (!list_empty(item)) {
+		list_del_init(item);
+		l->nr_items--;
+		atomic_long_dec(&lru->node[nid].nr_items);
+		return true;
+	}
+	return false;
+}
+
+/* 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_one *l;
+	bool ret;
+
+	l = list_lru_lock(lru, nid, memcg);
+	ret = __list_lru_add(lru, l, item, nid, memcg);
+	list_lru_unlock(l);
+	return ret;
+}
+
+bool list_lru_add_irq(struct list_lru *lru, struct list_head *item,
+		      int nid, struct mem_cgroup *memcg)
+{
+	struct list_lru_one *l;
+	bool ret;
+
+	l = list_lru_lock_irq(lru, nid, memcg);
+	ret = __list_lru_add(lru, l, item, nid, memcg);
+	list_lru_unlock_irq(l);
+	return ret;
+}
+
 bool list_lru_add_obj(struct list_lru *lru, struct list_head *item)
 {
 	bool ret;
@@ -185,19 +259,13 @@ 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;
+	bool ret;
 
-	l = lock_list_lru_of_memcg(lru, nid, memcg, false, 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;
+	l = list_lru_lock(lru, nid, memcg);
+	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)
@@ -270,7 +338,8 @@ __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=*/irq_off,
+				   /*irq_flags=*/NULL, /*skip_empty=*/true);
 	if (!l)
 		return isolated;
 	list_for_each_safe(item, n, &l->list) {
@@ -311,7 +380,7 @@ __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;
 }
-- 
2.54.0

[PATCH v4 6/8] mm: list_lru: introduce folio_memcg_list_lru_alloc()

[Johannes Weiner]

memcg_list_lru_alloc() is called every time an object that may end up
on the list_lru is created. It needs to quickly check if the list_lru
heads for the memcg already exist, and allocate them when they don't.

Doing this with folio objects is tricky: folio_memcg() is not stable
and requires either RCU protection or pinning the cgroup. But it's
desirable to make the existence check lightweight under RCU, and only
pin the memcg when we need to allocate list_lru heads and may block.

In preparation for switching the THP shrinker to list_lru, add a
helper function for allocating list_lru heads coming from a folio.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/list_lru.h | 27 +++++++++++++++++++++++++++
 mm/list_lru.c            | 39 ++++++++++++++++++++++++++++++++++-----
 2 files changed, 61 insertions(+), 5 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index c79ed378311f..733a262b91e5 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -81,6 +81,33 @@ 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
+/**
+ * folio_memcg_list_lru_alloc - allocate list_lru heads for shrinkable folio
+ * @folio: the newly allocated & charged folio
+ * @lru: the list_lru this might be queued on
+ * @gfp: gfp mask
+ *
+ * Allocate list_lru heads (per-memcg, per-node) needed to queue this
+ * particular folio down the line.
+ *
+ * This does memcg_list_lru_alloc(), but on the memcg that @folio is
+ * associated with. Handles folio_memcg() access rules in the fast
+ * path (list_lru heads allocated) and the allocation slowpath.
+ *
+ * Returns 0 on success, a negative error value otherwise.
+ */
+int folio_memcg_list_lru_alloc(struct folio *folio, struct list_lru *lru,
+			       gfp_t gfp);
+#else
+static inline int folio_memcg_list_lru_alloc(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);
 
 /**
diff --git a/mm/list_lru.c b/mm/list_lru.c
index df58226eea8c..4eeb4351c475 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -562,17 +562,14 @@ 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
@@ -613,6 +610,38 @@ 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 folio_memcg_list_lru_alloc(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();
+	memcg = folio_memcg(folio);
+	res = memcg_list_lru_allocated(memcg, lru);
+	rcu_read_unlock();
+	if (likely(res))
+		return 0;
+
+	/* Allocation may block, 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)
 {
-- 
2.54.0

[PATCH v4 7/8] mm/memory: flatten folio allocation retry loops

[Johannes Weiner]

alloc_swap_folio() and alloc_anon_folio() use a top-level if (folio)
that buries the success path four levels deep. This makes for awkward
long lines and wrapping. The next patch will add more code here, so
flatten this now to keep things clean and simple.

alloc_anon_folio() already has a next label, use it for !folio. Add
the equivalent to alloc_swap_folio().

No functional change intended.

Suggested-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memory.c | 44 +++++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 0c9d9c2cbf0e..552fe26a042a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4752,13 +4752,15 @@ 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;
 		}
+		return folio;
+next:
 		count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
 		order = next_order(&orders, order);
 	}
@@ -5270,24 +5272,24 @@ 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;
 		}
+		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);
-- 
2.54.0

[PATCH v4 8/8] 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
folio_memcg_alloc_deferred(). 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.

Reported-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Tested-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/huge_mm.h    |   7 +-
 include/linux/memcontrol.h |   4 -
 include/linux/mmzone.h     |  12 --
 mm/huge_memory.c           | 355 ++++++++++++-------------------------
 mm/internal.h              |   2 +-
 mm/khugepaged.c            |   3 +
 mm/memcontrol.c            |  12 +-
 mm/memory.c                |   8 +
 mm/mm_init.c               |  15 --
 9 files changed, 133 insertions(+), 285 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 127f9e1e7604..dc939873f5df 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -398,10 +398,10 @@ static inline int split_huge_page(struct page *page)
 {
 	return split_huge_page_to_list_to_order(page, NULL, 0);
 }
+
+int folio_memcg_alloc_deferred(struct folio *folio);
+
 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);
@@ -634,7 +634,6 @@ static inline int folio_split(struct folio *folio, unsigned int new_order,
 }
 
 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/memcontrol.h b/include/linux/memcontrol.h
index dc3fa687759b..4a7d8c4f55b4 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 1331a7b93f33..8e449f524f26 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1431,14 +1431,6 @@ 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.
@@ -1564,10 +1556,6 @@ 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 c565b2a651e0..67be09a58d5a 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 +68,8 @@ unsigned long transparent_hugepage_flags __read_mostly =
 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 
+static struct lock_class_key deferred_split_key;
+static 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);
@@ -943,6 +946,13 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 }
 #endif /* CONFIG_SYSFS */
 
+int folio_memcg_alloc_deferred(struct folio *folio)
+{
+	if (mem_cgroup_disabled())
+		return 0;
+	return folio_memcg_list_lru_alloc(folio, &deferred_split_lru, GFP_KERNEL);
+}
+
 static int __init thp_shrinker_init(void)
 {
 	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
@@ -952,6 +962,13 @@ static int __init thp_shrinker_init(void)
 	if (!deferred_split_shrinker)
 		return -ENOMEM;
 
+	if (list_lru_init_memcg_key(&deferred_split_lru,
+				    deferred_split_shrinker,
+				    &deferred_split_key)) {
+		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);
@@ -973,6 +990,7 @@ static int __init thp_shrinker_init(void)
 	huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero");
 	if (!huge_zero_folio_shrinker) {
 		shrinker_free(deferred_split_shrinker);
+		list_lru_destroy(&deferred_split_lru);
 		return -ENOMEM;
 	}
 
@@ -987,6 +1005,7 @@ static void __init thp_shrinker_exit(void)
 {
 	shrinker_free(huge_zero_folio_shrinker);
 	shrinker_free(deferred_split_shrinker);
+	list_lru_destroy(&deferred_split_lru);
 }
 
 static int __init hugepage_init(void)
@@ -1166,119 +1185,6 @@ 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))
@@ -1379,6 +1285,14 @@ 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 (folio_memcg_alloc_deferred(folio)) {
+		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);
 
        /*
@@ -3888,34 +3802,40 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
 	struct folio *end_folio = folio_next(folio);
 	struct folio *new_folio, *next;
 	int old_order = folio_order(folio);
+	struct list_lru_one *lru;
+	bool dequeue_deferred;
 	int ret = 0;
-	struct deferred_split *ds_queue;
 
 	VM_WARN_ON_ONCE(!mapping && end);
-	/* Prevent deferred_split_scan() touching ->_refcount */
-	ds_queue = folio_split_queue_lock(folio);
+	/*
+	 * If this folio can be on the deferred split queue, lock out
+	 * the shrinker before freezing the ref. If the shrinker sees
+	 * a 0-ref folio, it assumes it beat folio_put() to the list
+	 * lock and must clean up the LRU state - the same dequeue we
+	 * will do below as part of the split.
+	 */
+	dequeue_deferred = folio_test_anon(folio) && old_order > 1;
+	if (dequeue_deferred) {
+		rcu_read_lock();
+		lru = 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);
-			}
+		if (dequeue_deferred) {
+			__list_lru_del(&deferred_split_lru, lru,
+				       &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);
 			}
+			list_lru_unlock(lru);
+			rcu_read_unlock();
 		}
-		split_queue_unlock(ds_queue);
+
 		if (mapping) {
 			int nr = folio_nr_pages(folio);
 
@@ -4015,7 +3935,10 @@ 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);
+		if (dequeue_deferred) {
+			list_lru_unlock(lru);
+			rcu_read_unlock();
+		}
 		return -EAGAIN;
 	}
 
@@ -4381,33 +4304,35 @@ 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 *lru;
+	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();
+	lru = list_lru_lock_irqsave(&deferred_split_lru, nid, folio_memcg(folio), &flags);
+	if (__list_lru_del(&deferred_split_lru, lru, &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(lru, &flags);
+	rcu_read_unlock();
 
 	return unqueued;	/* useful for debug warnings */
 }
@@ -4415,7 +4340,9 @@ 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 *lru;
+	int nid;
+	struct mem_cgroup *memcg;
 	unsigned long flags;
 
 	/*
@@ -4438,7 +4365,11 @@ 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);
+	lru = list_lru_lock_irqsave(&deferred_split_lru, nid, memcg, &flags);
 	if (partially_mapped) {
 		if (!folio_test_partially_mapped(folio)) {
 			folio_set_partially_mapped(folio);
@@ -4446,36 +4377,20 @@ 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, lru, &folio->_deferred_list, nid, memcg);
+	list_lru_unlock_irqrestore(lru, &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)
@@ -4505,45 +4420,45 @@ 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;
 
-		folio = fbatch.folios[i];
+		list_del_init(&folio->_deferred_list);
+
 		if (!folio_test_partially_mapped(folio)) {
 			/*
 			 * See try_to_map_unused_to_zeropage(): we cannot
@@ -4572,63 +4487,23 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		 * underused, then consider it used and don't add it back to
 		 * split_queue.
 		 */
-		if (did_split || !folio_test_partially_mapped(folio))
-			continue;
+		if (!did_split && folio_test_partially_mapped(folio)) {
 requeue:
-		/*
-		 * Add back partially mapped folios, or underused folios that
-		 * we could not lock this round.
-		 */
-		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++;
+			rcu_read_lock();
+			list_lru_add_irq(&deferred_split_lru,
+					 &folio->_deferred_list,
+					 folio_nid(folio),
+					 folio_memcg(folio));
+			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 09931b1e535f..e5bf549ad78e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -861,7 +861,7 @@ 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 1a25af3d6d0f..644de0410c12 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1301,6 +1301,9 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long s
 	if (result != SCAN_SUCCEED)
 		goto out_nolock;
 
+	if (folio_memcg_alloc_deferred(folio))
+		goto out_nolock;
+
 	mmap_read_lock(mm);
 	result = hugepage_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true,
 					 &vma, cc, order);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aa7361b0d2da..fe896824078b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4065,11 +4065,6 @@ 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;
@@ -4221,11 +4216,10 @@ 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 552fe26a042a..b97e3145982a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4759,6 +4759,10 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
 			folio_put(folio);
 			goto next;
 		}
+		if (order > 1 && folio_memcg_alloc_deferred(folio)) {
+			folio_put(folio);
+			goto fallback;
+		}
 		return folio;
 next:
 		count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
@@ -5279,6 +5283,10 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 			folio_put(folio);
 			goto next;
 		}
+		if (order > 1 && folio_memcg_alloc_deferred(folio)) {
+			folio_put(folio);
+			goto fallback;
+		}
 		folio_throttle_swaprate(folio, gfp);
 		/*
 		 * When a folio is not zeroed during allocation
diff --git a/mm/mm_init.c b/mm/mm_init.c
index db5568cf36e1..c0a7f1cf6fef 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1373,19 +1373,6 @@ 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)
 {
@@ -1401,8 +1388,6 @@ 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);
-- 
2.54.0

Re: [PATCH v4 7/8] mm/memory: flatten folio allocation retry loops

[Shakeel Butt]

On Thu, May 21, 2026 at 11:02:13AM -0400, Johannes Weiner wrote:
> alloc_swap_folio() and alloc_anon_folio() use a top-level if (folio)
> that buries the success path four levels deep. This makes for awkward
> long lines and wrapping. The next patch will add more code here, so
> flatten this now to keep things clean and simple.
> 
> alloc_anon_folio() already has a next label, use it for !folio. Add
> the equivalent to alloc_swap_folio().
> 
> No functional change intended.
> 
> Suggested-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH v4 1/8] mm: list_lru: lock_list_lru_of_memcg() cannot return NULL if !skip_empty

[Liam R . Howlett]

On 26/05/21 11:02AM, Johannes Weiner wrote:
> skip_empty is only for the shrinker to abort and skip a list that's
> empty or whose cgroup is being deleted.
> 
> For list additions and deletions, the cgroup hierarchy is walked
> upwards until a valid list_lru head is found, or it will fall back to
> the node list. Acquiring the lock won't fail. Remove the NULL checks
> in those callers.
> 
> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Liam R. Howlett (Oracle) <liam@infradead.org>

> ---
>  mm/list_lru.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index dd29bcf8eb5f..d3619961a7ac 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -165,8 +165,6 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
>  	struct list_lru_one *l;
>  
>  	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> -	if (!l)
> -		return false;
>  	if (list_empty(item)) {
>  		list_add_tail(item, &l->list);
>  		/* Set shrinker bit if the first element was added */
> @@ -204,9 +202,8 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
>  {
>  	struct list_lru_node *nlru = &lru->node[nid];
>  	struct list_lru_one *l;
> +
>  	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> -	if (!l)
> -		return false;
>  	if (!list_empty(item)) {
>  		list_del_init(item);
>  		l->nr_items--;
> -- 
> 2.54.0
> 

Re: [PATCH v4 2/8] mm: list_lru: deduplicate unlock_list_lru()

[Liam R . Howlett]

On 26/05/21 11:02AM, Johannes Weiner wrote:
> The MEMCG and !MEMCG variants are the same. lock_list_lru() has the
> same pattern when bailing. Consolidate into a common implementation.
> 
> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Liam R. Howlett (Oracle) <liam@infradead.org>

> ---
>  mm/list_lru.c | 29 +++++++++--------------------
>  1 file changed, 9 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index d3619961a7ac..9a68177619bf 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -15,6 +15,14 @@
>  #include "slab.h"
>  #include "internal.h"
>  
> +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);
> +}
> +
>  #ifdef CONFIG_MEMCG
>  static LIST_HEAD(memcg_list_lrus);
>  static DEFINE_MUTEX(list_lrus_mutex);
> @@ -67,10 +75,7 @@ static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
>  	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);
> +		unlock_list_lru(l, irq);
>  		return false;
>  	}
>  	return true;
> @@ -101,14 +106,6 @@ 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)
>  {
> @@ -147,14 +144,6 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  
>  	return l;
>  }
> -
> -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);
> -}
>  #endif /* CONFIG_MEMCG */
>  
>  /* The caller must ensure the memcg lifetime. */
> -- 
> 2.54.0
> 

Re: [PATCH v4 3/8] mm: list_lru: move list dead check to lock_list_lru_of_memcg()

[Liam R . Howlett]

On 26/05/21 11:02AM, Johannes Weiner wrote:
> Only the MEMCG variant of lock_list_lru() needs to check if there is a
> race with cgroup deletion and list reparenting. Move the check to the
> caller, so that the next patch can unify the lock_list_lru() variants.
> 
> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Liam R. Howlett (Oracle) <liam@infradead.org>

> ---
>  mm/list_lru.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 9a68177619bf..9da6fce19832 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -68,17 +68,12 @@ 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)
> +static inline void 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)) {
> -		unlock_list_lru(l, irq);
> -		return false;
> -	}
> -	return true;
>  }
>  
>  static inline struct list_lru_one *
> @@ -90,9 +85,13 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  	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);
> +		if (likely(READ_ONCE(l->nr_items) != LONG_MIN)) {
> +			rcu_read_unlock();
> +			return l;
> +		}
> +		unlock_list_lru(l, irq);
>  	}
>  	/*
>  	 * Caller may simply bail out if raced with reparenting or
> -- 
> 2.54.0
> 

Re: [PATCH v4 4/8] mm: list_lru: deduplicate lock_list_lru()

[Liam R . Howlett]

On 26/05/21 11:02AM, Johannes Weiner wrote:
> The MEMCG and !MEMCG paths have the same pattern. Share the code.
> 
> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Liam R. Howlett (Oracle) <liam@infradead.org>

> ---
>  mm/list_lru.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 9da6fce19832..65962dbf6dda 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -15,6 +15,14 @@
>  #include "slab.h"
>  #include "internal.h"
>  
> +static inline void lock_list_lru(struct list_lru_one *l, bool irq)
> +{
> +	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_off)
>  {
>  	if (irq_off)
> @@ -68,14 +76,6 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
>  	return &lru->node[nid].lru;
>  }
>  
> -static inline void lock_list_lru(struct list_lru_one *l, bool irq)
> -{
> -	if (irq)
> -		spin_lock_irq(&l->lock);
> -	else
> -		spin_lock(&l->lock);
> -}
> -
>  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)
> @@ -136,10 +136,7 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  {
>  	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);
>  
>  	return l;
>  }
> -- 
> 2.54.0
> 

Re: [PATCH v4 5/8] mm: list_lru: introduce caller locking for additions and deletions

[Liam R . Howlett]

On 26/05/21 11:02AM, Johannes Weiner wrote:
> Locking is currently internal to the list_lru API. However, a caller
> might want to keep auxiliary state synchronized with the LRU state.
> 
> For example, the THP shrinker uses the lock of its custom LRU to keep
> PG_partially_mapped and vmstats consistent.
> 
> To allow the THP shrinker to switch to list_lru, provide normal and
> irqsafe locking primitives as well as caller-locked variants of the
> addition and deletion functions.
> 
> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Liam R. Howlett (Oracle) <liam@infradead.org>

> ---
>  include/linux/list_lru.h |  41 ++++++++++++
>  mm/list_lru.c            | 131 ++++++++++++++++++++++++++++++---------
>  2 files changed, 141 insertions(+), 31 deletions(-)
> 
> diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> index fe739d35a864..c79ed378311f 100644
> --- a/include/linux/list_lru.h
> +++ b/include/linux/list_lru.h
> @@ -83,6 +83,44 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
>  			 gfp_t gfp);
>  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_irq(struct list_lru *lru, int nid,
> +		struct mem_cgroup *memcg);
> +void list_lru_unlock_irq(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
> @@ -115,6 +153,9 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
>  bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
>  		    struct mem_cgroup *memcg);
>  
> +bool list_lru_add_irq(struct list_lru *lru, struct list_head *item, int nid,
> +		      struct mem_cgroup *memcg);
> +
>  /**
>   * list_lru_add_obj: add an element to the lru list's tail
>   * @lru: the lru pointer
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 65962dbf6dda..df58226eea8c 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -15,17 +15,23 @@
>  #include "slab.h"
>  #include "internal.h"
>  
> -static inline void lock_list_lru(struct list_lru_one *l, bool irq)
> +static inline void lock_list_lru(struct list_lru_one *l, bool irq,
> +				 unsigned long *irq_flags)
>  {
> -	if (irq)
> +	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_off)
> +static inline void unlock_list_lru(struct list_lru_one *l, bool irq_off,
> +				   unsigned long *irq_flags)
>  {
> -	if (irq_off)
> +	if (irq_flags)
> +		spin_unlock_irqrestore(&l->lock, *irq_flags);
> +	else if (irq_off)
>  		spin_unlock_irq(&l->lock);
>  	else
>  		spin_unlock(&l->lock);
> @@ -78,7 +84,7 @@ 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;
>  
> @@ -86,12 +92,12 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  again:
>  	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
>  	if (likely(l)) {
> -		lock_list_lru(l, irq);
> +		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);
> +		unlock_list_lru(l, irq, irq_flags);
>  	}
>  	/*
>  	 * Caller may simply bail out if raced with reparenting or
> @@ -132,38 +138,106 @@ 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;
>  
> -	lock_list_lru(l, irq);
> +	lock_list_lru(l, irq, irq_flags);
>  
>  	return l;
>  }
>  #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_one *list_lru_lock(struct list_lru *lru, int nid,
> +				   struct mem_cgroup *memcg)
>  {
> -	struct list_lru_node *nlru = &lru->node[nid];
> -	struct list_lru_one *l;
> +	return lock_list_lru_of_memcg(lru, nid, memcg, /*irq=*/false,
> +				      /*irq_flags=*/NULL, /*skip_empty=*/false);
> +}
> +
> +void list_lru_unlock(struct list_lru_one *l)
> +{
> +	unlock_list_lru(l, /*irq_off=*/false, /*irq_flags=*/NULL);
> +}
> +
> +struct list_lru_one *list_lru_lock_irq(struct list_lru *lru, int nid,
> +				       struct mem_cgroup *memcg)
> +{
> +	return lock_list_lru_of_memcg(lru, nid, memcg, /*irq=*/true,
> +				      /*irq_flags=*/NULL, /*skip_empty=*/false);
> +}
> +
> +void list_lru_unlock_irq(struct list_lru_one *l)
> +{
> +	unlock_list_lru(l, /*irq_off=*/true, /*irq_flags=*/NULL);
> +}
>  
> -	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> +struct list_lru_one *list_lru_lock_irqsave(struct list_lru *lru, int nid,
> +					   struct mem_cgroup *memcg,
> +					   unsigned long *flags)
> +{
> +	return lock_list_lru_of_memcg(lru, nid, memcg, /*irq=*/true,
> +				      /*irq_flags=*/flags, /*skip_empty=*/false);
> +}
> +
> +void list_lru_unlock_irqrestore(struct list_lru_one *l, unsigned long *flags)
> +{
> +	unlock_list_lru(l, /*irq_off=*/true, /*irq_flags=*/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)) {
>  		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);
> +		atomic_long_inc(&lru->node[nid].nr_items);
>  		return true;
>  	}
> -	unlock_list_lru(l, false);
>  	return false;
>  }
>  EXPORT_SYMBOL_GPL(list_lru_add);
>  
> +bool __list_lru_del(struct list_lru *lru, struct list_lru_one *l,
> +		    struct list_head *item, int nid)
> +{
> +	if (!list_empty(item)) {
> +		list_del_init(item);
> +		l->nr_items--;
> +		atomic_long_dec(&lru->node[nid].nr_items);
> +		return true;
> +	}
> +	return false;
> +}
> +
> +/* 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_one *l;
> +	bool ret;
> +
> +	l = list_lru_lock(lru, nid, memcg);
> +	ret = __list_lru_add(lru, l, item, nid, memcg);
> +	list_lru_unlock(l);
> +	return ret;
> +}
> +
> +bool list_lru_add_irq(struct list_lru *lru, struct list_head *item,
> +		      int nid, struct mem_cgroup *memcg)
> +{
> +	struct list_lru_one *l;
> +	bool ret;
> +
> +	l = list_lru_lock_irq(lru, nid, memcg);
> +	ret = __list_lru_add(lru, l, item, nid, memcg);
> +	list_lru_unlock_irq(l);
> +	return ret;
> +}
> +
>  bool list_lru_add_obj(struct list_lru *lru, struct list_head *item)
>  {
>  	bool ret;
> @@ -185,19 +259,13 @@ 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;
> +	bool ret;
>  
> -	l = lock_list_lru_of_memcg(lru, nid, memcg, false, 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;
> +	l = list_lru_lock(lru, nid, memcg);
> +	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)
> @@ -270,7 +338,8 @@ __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=*/irq_off,
> +				   /*irq_flags=*/NULL, /*skip_empty=*/true);
>  	if (!l)
>  		return isolated;
>  	list_for_each_safe(item, n, &l->list) {
> @@ -311,7 +380,7 @@ __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;
>  }
> -- 
> 2.54.0
>