[PATCH v2] net: iterate online nodes in skb_defer_free_flush()

[Kris Pan]

skb_attempt_defer_free() only queues skbs on the current CPU's node
(numa_node_id() of a running CPU), which is always online, so the
flush loop never needs to visit nodes that are merely possible.

for_each_node() walks node_possible_map.  On machines where the
possible map is much larger than the online map -- e.g. a POWER10
LPAR with 32 possible but 1 online node -- the flush loop touches 31
cold, always-empty per-node lists on every softirq pass, showing up
as skb_defer_free_flush() and _find_next_bit() overhead.

Use for_each_online_node() to iterate only node_online_map.

Loopback UDP throughput in a QEMU guest with 32 possible / 1 online
nodes (bench_udp, 8 senders, 6 interleaved runs) improves by ~5%.

Fixes: 5628f3fe3b16 ("net: add NUMA awareness to skb_attempt_defer_free()")
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Suggested-by: Adrian Tomasov <atomasov@xxxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202512112119.5b9829a-lkp@xxxxxxxxx
Signed-off-by: Kris Pan <kris.pan@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 290e0f099e6bf..b528b6a986fcf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6907,7 +6907,7 @@ static void skb_defer_free_flush(void)
 	struct skb_defer_node *sdn;
 	int node;
 
-	for_each_node(node) {
+	for_each_online_node(node) {
 		sdn = this_cpu_ptr(net_hotdata.skb_defer_nodes) + node;
 
 		if (llist_empty(&sdn->defer_list))
-- 
2.43.0