Subject: [net-next PATCH V2 2/3] net: bulk free SKBs that were delay free'ed due to IRQ context

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 08 Feb 2016 13:15:04 +0100

The network stack defers SKBs free, in-case free happens in IRQ or
when IRQs are disabled. This happens in __dev_kfree_skb_irq() that
writes SKBs that were free'ed during IRQ to the softirq completion
queue (softnet_data.completion_queue).

These SKBs are naturally delayed, and cleaned up during NET_TX_SOFTIRQ
in function net_tx_action().  Take advantage of this a use the skb
defer and flush API, as we are already in softirq context.

For modern drivers this rarely happens. Although most drivers do call
dev_kfree_skb_any(), which detects the situation and calls
__dev_kfree_skb_irq() when needed.  This due to netpoll can call from
IRQ context.

Signed-off-by: Alexander Duyck <[email-masked]>
Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
---
 include/linux/skbuff.h |    1 +
 net/core/dev.c         |    8 +++++++-
 net/core/skbuff.c      |    8 ++++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3c8d348223d7..b06ba2e07c89 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2402,6 +2402,7 @@ static inline struct sk_buff *napi_alloc_skb(struct napi_struct *napi,
 void napi_consume_skb(struct sk_buff *skb, int budget);
 
 void __kfree_skb_flush(void);
+void __kfree_skb_defer(struct sk_buff *skb);
 
 /**
  * __dev_alloc_pages - allocate page for network Rx
diff --git a/net/core/dev.c b/net/core/dev.c
index 44384a8c9613..b185d7eaa2e4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3829,8 +3829,14 @@ static void net_tx_action(struct softirq_action *h)
 				trace_consume_skb(skb);
 			else
 				trace_kfree_skb(skb, net_tx_action);
-			__kfree_skb(skb);
+
+			if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
+				__kfree_skb(skb);
+			else
+				__kfree_skb_defer(skb);
 		}
+
+		__kfree_skb_flush();
 	}
 
 	if (sd->output_queue) {
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index e26bb2b1dba4..d278e51789e9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -767,7 +767,7 @@ void __kfree_skb_flush(void)
 	}
 }
 
-static void __kfree_skb_defer(struct sk_buff *skb)
+static inline void _kfree_skb_defer(struct sk_buff *skb)
 {
 	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
 
@@ -789,6 +789,10 @@ static void __kfree_skb_defer(struct sk_buff *skb)
 		nc->skb_count = 0;
 	}
 }
+void __kfree_skb_defer(struct sk_buff *skb)
+{
+	_kfree_skb_defer(skb);
+}
 
 void napi_consume_skb(struct sk_buff *skb, int budget)
 {
@@ -814,7 +818,7 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
 		return;
 	}
 
-	__kfree_skb_defer(skb);
+	_kfree_skb_defer(skb);
 }
 EXPORT_SYMBOL(napi_consume_skb);

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