[PATCH v1 net-next 3/4] neighbour: Schedule neigh_managed_work only when needed.

[Kuniyuki Iwashima <kuniyu@google.com>]

neigh_table is now per-netns.

tbl->managed_work is scheduled when netns is created and runs
periodically even though the netns does not have any NTF_MANAGED
entries.

Let's delay scheduling the work for the first NTF_MANAGED entry
and stop rescheduling if tbl->managed_list is empty.

Suggested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/core/neighbour.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 90335895b415..6b0569aa5d64 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -184,6 +184,15 @@ static void neigh_update_gc_list(struct neighbour *n)
 	}
 }
 
+static void neigh_add_managed_list(struct neighbour *n)
+{
+	list_add_tail(&n->managed_list, &n->tbl->managed_list);
+
+	if (list_is_singular(&n->tbl->managed_list))
+		queue_delayed_work(system_power_efficient_wq,
+				   &n->tbl->managed_work, 0);
+}
+
 static void neigh_update_managed_list(struct neighbour *n)
 {
 	bool on_managed_list, add_to_managed;
@@ -194,7 +203,7 @@ static void neigh_update_managed_list(struct neighbour *n)
 	if (!add_to_managed && on_managed_list)
 		list_del_init(&n->managed_list);
 	else if (add_to_managed && !on_managed_list)
-		list_add_tail(&n->managed_list, &n->tbl->managed_list);
+		neigh_add_managed_list(n);
 }
 
 static void neigh_update_flags(struct neighbour *neigh, u32 flags, int *notify,
@@ -708,7 +717,7 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 	if (!exempt_from_gc)
 		list_add_tail(&n->gc_list, &n->tbl->gc_list);
 	if (n->flags & NTF_MANAGED)
-		list_add_tail(&n->managed_list, &n->tbl->managed_list);
+		neigh_add_managed_list(n);
 	if (want_ref)
 		neigh_hold(n);
 	hlist_add_head_rcu(&n->hash, &nht->hash_heads[hash_val]);
@@ -1670,10 +1679,14 @@ static void neigh_managed_work(struct work_struct *work)
 	struct neighbour *neigh;
 
 	spin_lock_bh(&tbl->lock);
+
 	list_for_each_entry(neigh, &tbl->managed_list, managed_list)
 		neigh_event_send_probe(neigh, NULL, false);
-	queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
-			   NEIGH_VAR(&tbl->parms, INTERVAL_PROBE_TIME_MS));
+
+	if (!list_empty(&tbl->managed_list))
+		queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
+				   NEIGH_VAR(&tbl->parms, INTERVAL_PROBE_TIME_MS));
+
 	spin_unlock_bh(&tbl->lock);
 }
 
@@ -1873,7 +1886,6 @@ static int neigh_table_init(struct net *net, struct neigh_table *tbl)
 
 	INIT_LIST_HEAD(&tbl->managed_list);
 	INIT_DEFERRABLE_WORK(&tbl->managed_work, neigh_managed_work);
-	queue_delayed_work(system_power_efficient_wq, &tbl->managed_work, 0);
 
 	return 0;
 
-- 
2.56.0.385.gd3acb90ef8-goog