[PATCH v4 25/31] mm: vmscan: prepare for reparenting traditional LRU folios

[Qi Zheng <qi.zheng@linux.dev>]

From: Qi Zheng <zhengqi.arch@bytedance.com>

To resolve the dying memcg issue, we need to reparent LRU folios of child
memcg to its parent memcg. For traditional LRU list, each lruvec of every
memcg comprises four LRU lists. Due to the symmetry of the LRU lists, it
is feasible to transfer the LRU lists from a memcg to its parent memcg
during the reparenting process.

This commit implements the specific function, which will be used during
the reparenting process.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Muchun Song <muchun.song@linux.dev>
---
 include/linux/swap.h | 21 +++++++++++++++++++++
 mm/swap.c            | 37 +++++++++++++++++++++++++++++++++++++
 mm/vmscan.c          | 19 -------------------
 3 files changed, 58 insertions(+), 19 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 39ecd25217178..62e124ec6b75a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -570,6 +570,8 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 
 	return READ_ONCE(memcg->swappiness);
 }
+
+void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent);
 #else
 static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 {
@@ -634,5 +636,24 @@ static inline bool mem_cgroup_swap_full(struct folio *folio)
 }
 #endif
 
+/* for_each_managed_zone_pgdat - helper macro to iterate over all managed zones in a pgdat up to
+ * and including the specified highidx
+ * @zone: The current zone in the iterator
+ * @pgdat: The pgdat which node_zones are being iterated
+ * @idx: The index variable
+ * @highidx: The index of the highest zone to return
+ *
+ * This macro iterates through all managed zones up to and including the specified highidx.
+ * The zone iterator enters an invalid state after macro call and must be reinitialized
+ * before it can be used again.
+ */
+#define for_each_managed_zone_pgdat(zone, pgdat, idx, highidx)	\
+	for ((idx) = 0, (zone) = (pgdat)->node_zones;		\
+	    (idx) <= (highidx);					\
+	    (idx)++, (zone)++)					\
+		if (!managed_zone(zone))			\
+			continue;				\
+		else
+
 #endif /* __KERNEL__*/
 #endif /* _LINUX_SWAP_H */
diff --git a/mm/swap.c b/mm/swap.c
index d5bfe6a76ca45..25f39d4263fb5 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -1090,6 +1090,43 @@ void folio_batch_remove_exceptionals(struct folio_batch *fbatch)
 	fbatch->nr = j;
 }
 
+#ifdef CONFIG_MEMCG
+static void lruvec_reparent_lru(struct lruvec *child_lruvec,
+				struct lruvec *parent_lruvec,
+				enum lru_list lru, int nid)
+{
+	int zid;
+	struct zone *zone;
+
+	if (lru != LRU_UNEVICTABLE)
+		list_splice_tail_init(&child_lruvec->lists[lru], &parent_lruvec->lists[lru]);
+
+	for_each_managed_zone_pgdat(zone, NODE_DATA(nid), zid, MAX_NR_ZONES - 1) {
+		unsigned long size = mem_cgroup_get_zone_lru_size(child_lruvec, lru, zid);
+
+		mem_cgroup_update_lru_size(parent_lruvec, lru, zid, size);
+	}
+}
+
+void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
+	int nid;
+
+	for_each_node(nid) {
+		enum lru_list lru;
+		struct lruvec *child_lruvec, *parent_lruvec;
+
+		child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+		parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid));
+		parent_lruvec->anon_cost += child_lruvec->anon_cost;
+		parent_lruvec->file_cost += child_lruvec->file_cost;
+
+		for_each_lru(lru)
+			lruvec_reparent_lru(child_lruvec, parent_lruvec, lru, nid);
+	}
+}
+#endif
+
 static const struct ctl_table swap_sysctl_table[] = {
 	{
 		.procname	= "page-cluster",
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f904231e33ec0..e2d9ef9a5dedc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -269,25 +269,6 @@ static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
 }
 #endif
 
-/* for_each_managed_zone_pgdat - helper macro to iterate over all managed zones in a pgdat up to
- * and including the specified highidx
- * @zone: The current zone in the iterator
- * @pgdat: The pgdat which node_zones are being iterated
- * @idx: The index variable
- * @highidx: The index of the highest zone to return
- *
- * This macro iterates through all managed zones up to and including the specified highidx.
- * The zone iterator enters an invalid state after macro call and must be reinitialized
- * before it can be used again.
- */
-#define for_each_managed_zone_pgdat(zone, pgdat, idx, highidx)	\
-	for ((idx) = 0, (zone) = (pgdat)->node_zones;		\
-	    (idx) <= (highidx);					\
-	    (idx)++, (zone)++)					\
-		if (!managed_zone(zone))			\
-			continue;				\
-		else
-
 static void set_task_reclaim_state(struct task_struct *task,
 				   struct reclaim_state *rs)
 {
-- 
2.20.1