net: netpoll: Individualize the skb pool

The current implementation of the netpoll system uses a global skb
pool, which can lead to inefficient memory usage and
waste when targets are disabled or no longer in use.

This can result in a significant amount of memory being unnecessarily
allocated and retained, potentially causing performance issues and
limiting the availability of resources for other system components.

Modify the netpoll system to assign a skb pool to each target instead of
using a global one.

This approach allows for more fine-grained control over memory
allocation and deallocation, ensuring that resources are only allocated
and retained as needed.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20241114-skb_buffers_v2-v3-1-9be9f52a8b69@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netpoll.h

@@ -32,6 +32,7 @@ struct netpoll {
 	bool ipv6;
 	u16 local_port, remote_port;
 	u8 remote_mac[ETH_ALEN];
+	struct sk_buff_head skb_pool;
 };
 
 struct netpoll_info {

net/core/netpoll.c

@@ -45,9 +45,6 @@
 
 #define MAX_UDP_CHUNK 1460
 #define MAX_SKBS 32
-
-static struct sk_buff_head skb_pool;
-
 #define USEC_PER_POLL	50
 
 #define MAX_SKB_SIZE							\
@@ -234,20 +231,23 @@ void netpoll_poll_enable(struct net_device *dev)
 		up(&ni->dev_lock);
 }
 
-static void refill_skbs(void)
+static void refill_skbs(struct netpoll *np)
 {
+	struct sk_buff_head *skb_pool;
 	struct sk_buff *skb;
 	unsigned long flags;
 
-	spin_lock_irqsave(&skb_pool.lock, flags);
-	while (skb_pool.qlen < MAX_SKBS) {
+	skb_pool = &np->skb_pool;
+
+	spin_lock_irqsave(&skb_pool->lock, flags);
+	while (skb_pool->qlen < MAX_SKBS) {
 		skb = alloc_skb(MAX_SKB_SIZE, GFP_ATOMIC);
 		if (!skb)
 			break;
 
-		__skb_queue_tail(&skb_pool, skb);
+		__skb_queue_tail(skb_pool, skb);
 	}
-	spin_unlock_irqrestore(&skb_pool.lock, flags);
+	spin_unlock_irqrestore(&skb_pool->lock, flags);
 }
 
 static void zap_completion_queue(void)
@@ -284,12 +284,12 @@ static struct sk_buff *find_skb(struct netpoll *np, int len, int reserve)
 	struct sk_buff *skb;
 
 	zap_completion_queue();
-	refill_skbs();
+	refill_skbs(np);
 repeat:
 
 	skb = alloc_skb(len, GFP_ATOMIC);
 	if (!skb)
-		skb = skb_dequeue(&skb_pool);
+		skb = skb_dequeue(&np->skb_pool);
 
 	if (!skb) {
 		if (++count < 10) {
@@ -673,6 +673,8 @@ int netpoll_setup(struct netpoll *np)
 	struct in_device *in_dev;
 	int err;
 
+	skb_queue_head_init(&np->skb_pool);
+
 	rtnl_lock();
 	if (np->dev_name[0]) {
 		struct net *net = current->nsproxy->net_ns;
@@ -773,7 +775,7 @@ int netpoll_setup(struct netpoll *np)
 	}
 
 	/* fill up the skb queue */
-	refill_skbs();
+	refill_skbs(np);
 
 	err = __netpoll_setup(np, ndev);
 	if (err)
@@ -792,13 +794,6 @@ int netpoll_setup(struct netpoll *np)
 }
 EXPORT_SYMBOL(netpoll_setup);
 
-static int __init netpoll_init(void)
-{
-	skb_queue_head_init(&skb_pool);
-	return 0;
-}
-core_initcall(netpoll_init);
-
 static void rcu_cleanup_netpoll_info(struct rcu_head *rcu_head)
 {
 	struct netpoll_info *npinfo =