mm: thp: introduce folio_split_queue_lock and its variants

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

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

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

Link: https://lkml.kernel.org/r/a31a90bcac04dc754f775e87ae3205be3170b571.1762762324.git.zhengqi.arch@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nico Pache <npache@redhat.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 84 insertions, 35 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9758171d49c9..bfcb5d895f67 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1077,28 +1077,86 @@ 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 deferred_split *get_deferred_split_queue(struct folio *folio)
+struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
+					   struct deferred_split *queue)
 {
-	struct mem_cgroup *memcg = folio_memcg(folio);
-	struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
+	if (mem_cgroup_disabled())
+		return NULL;
+	if (split_queue_node(folio_nid(folio)) == queue)
+		return NULL;
+	return container_of(queue, struct mem_cgroup, deferred_split_queue);
+}
 
-	if (memcg)
-		return &memcg->deferred_split_queue;
-	else
-		return &pgdat->deferred_split_queue;
+static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memcg)
+{
+	return memcg ? &memcg->deferred_split_queue : split_queue_node(nid);
 }
 #else
 static inline
-struct deferred_split *get_deferred_split_queue(struct folio *folio)
+struct mem_cgroup *folio_split_queue_memcg(struct folio *folio,
+					   struct deferred_split *queue)
 {
-	struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
+	return NULL;
+}
 
-	return &pgdat->deferred_split_queue;
+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;
+
+	queue = memcg_split_queue(nid, memcg);
+	spin_lock(&queue->split_queue_lock);
+
+	return queue;
+}
+
+static struct deferred_split *
+split_queue_lock_irqsave(int nid, struct mem_cgroup *memcg, unsigned long *flags)
+{
+	struct deferred_split *queue;
+
+	queue = memcg_split_queue(nid, memcg);
+	spin_lock_irqsave(&queue->split_queue_lock, *flags);
+
+	return queue;
+}
+
+static struct deferred_split *folio_split_queue_lock(struct folio *folio)
+{
+	return split_queue_lock(folio_nid(folio), folio_memcg(folio));
+}
+
+static struct deferred_split *
+folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
+{
+	return split_queue_lock_irqsave(folio_nid(folio), folio_memcg(folio), flags);
+}
+
+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))
@@ -3690,7 +3748,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 		struct page *split_at, struct page *lock_at,
 		struct list_head *list, enum split_type split_type, bool unmapped)
 {
-	struct deferred_split *ds_queue = get_deferred_split_queue(folio);
+	struct deferred_split *ds_queue;
 	XA_STATE(xas, &folio->mapping->i_pages, folio->index);
 	struct folio *end_folio = folio_next(folio);
 	bool is_anon = folio_test_anon(folio);
@@ -3824,7 +3882,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 	}
 
 	/* Prevent deferred_split_scan() touching ->_refcount */
-	spin_lock(&ds_queue->split_queue_lock);
+	ds_queue = folio_split_queue_lock(folio);
 	if (folio_ref_freeze(folio, 1 + extra_pins)) {
 		struct swap_cluster_info *ci = NULL;
 		struct lruvec *lruvec;
@@ -3846,7 +3904,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 			 */
 			list_del_init(&folio->_deferred_list);
 		}
-		spin_unlock(&ds_queue->split_queue_lock);
+		split_queue_unlock(ds_queue);
 		if (mapping) {
 			int nr = folio_nr_pages(folio);
 
@@ -3946,7 +4004,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 		if (ci)
 			swap_cluster_unlock(ci);
 	} else {
-		spin_unlock(&ds_queue->split_queue_lock);
+		split_queue_unlock(ds_queue);
 		ret = -EAGAIN;
 	}
 fail:
@@ -4129,8 +4187,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
 	WARN_ON_ONCE(folio_ref_count(folio));
 	WARN_ON_ONCE(!mem_cgroup_disabled() && !folio_memcg_charged(folio));
 
-	ds_queue = get_deferred_split_queue(folio);
-	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+	ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
 	if (!list_empty(&folio->_deferred_list)) {
 		ds_queue->split_queue_len--;
 		if (folio_test_partially_mapped(folio)) {
@@ -4141,7 +4198,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
 		list_del_init(&folio->_deferred_list);
 		unqueued = true;
 	}
-	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
+	split_queue_unlock_irqrestore(ds_queue, flags);
 
 	return unqueued;	/* useful for debug warnings */
 }
@@ -4149,10 +4206,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
 /* partially_mapped=false won't clear PG_partially_mapped folio flag */
 void deferred_split_folio(struct folio *folio, bool partially_mapped)
 {
-	struct deferred_split *ds_queue = get_deferred_split_queue(folio);
-#ifdef CONFIG_MEMCG
-	struct mem_cgroup *memcg = folio_memcg(folio);
-#endif
+	struct deferred_split *ds_queue;
 	unsigned long flags;
 
 	/*
@@ -4175,7 +4229,7 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 	if (folio_test_swapcache(folio))
 		return;
 
-	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+	ds_queue = folio_split_queue_lock_irqsave(folio, &flags);
 	if (partially_mapped) {
 		if (!folio_test_partially_mapped(folio)) {
 			folio_set_partially_mapped(folio);
@@ -4190,15 +4244,16 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 		VM_WARN_ON_FOLIO(folio_test_partially_mapped(folio), folio);
 	}
 	if (list_empty(&folio->_deferred_list)) {
+		struct mem_cgroup *memcg;
+
+		memcg = folio_split_queue_memcg(folio, ds_queue);
 		list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
 		ds_queue->split_queue_len++;
-#ifdef CONFIG_MEMCG
 		if (memcg)
 			set_shrinker_bit(memcg, folio_nid(folio),
-					 deferred_split_shrinker->id);
-#endif
+					 shrinker_id(deferred_split_shrinker));
 	}
-	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
+	split_queue_unlock_irqrestore(ds_queue, flags);
 }
 
 static unsigned long deferred_split_count(struct shrinker *shrink,
@@ -4244,19 +4299,13 @@ static bool thp_underused(struct folio *folio)
 static unsigned long deferred_split_scan(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
-	struct pglist_data *pgdata = NODE_DATA(sc->nid);
-	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
+	struct deferred_split *ds_queue;
 	unsigned long flags;
 	LIST_HEAD(list);
 	struct folio *folio, *next, *prev = NULL;
 	int split = 0, removed = 0;
 
-#ifdef CONFIG_MEMCG
-	if (sc->memcg)
-		ds_queue = &sc->memcg->deferred_split_queue;
-#endif
-
-	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+	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) {
@@ -4275,7 +4324,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		if (!--sc->nr_to_scan)
 			break;
 	}
-	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
+	split_queue_unlock_irqrestore(ds_queue, flags);
 
 	list_for_each_entry_safe(folio, next, &list, _deferred_list) {
 		bool did_split = false;