[RFC PATCH v2 net-next 05/12] net: core: another layer of lists, around PF_MEMALLOC skb handling

[Edward Cree <ecree@solarflare.com>]

First example of a layer splitting the list (rather than merely taking
 individual packets off it).

Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 net/core/dev.c | 46 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 27980c13ad5c..92d78b3de656 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4670,6 +4670,14 @@ int netif_receive_skb_core(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(netif_receive_skb_core);
 
+static void __netif_receive_skb_list_core(struct sk_buff_head *list, bool pfmemalloc)
+{
+	struct sk_buff *skb;
+
+	while ((skb = __skb_dequeue(list)) != NULL)
+		__netif_receive_skb_core(skb, pfmemalloc);
+}
+
 static int __netif_receive_skb(struct sk_buff *skb)
 {
 	int ret;
@@ -4695,6 +4703,36 @@ static int __netif_receive_skb(struct sk_buff *skb)
 	return ret;
 }
 
+static void __netif_receive_skb_list(struct sk_buff_head *list)
+{
+	unsigned long noreclaim_flag = 0;
+	struct sk_buff_head sublist;
+	bool pfmemalloc = false; /* Is current sublist PF_MEMALLOC? */
+	struct sk_buff *skb;
+
+	__skb_queue_head_init(&sublist);
+
+	while ((skb = __skb_dequeue(list)) != NULL) {
+		if ((sk_memalloc_socks() && skb_pfmemalloc(skb)) != pfmemalloc) {
+			/* Handle the previous sublist */
+			__netif_receive_skb_list_core(&sublist, pfmemalloc);
+			pfmemalloc = !pfmemalloc;
+			/* See comments in __netif_receive_skb */
+			if (pfmemalloc)
+				noreclaim_flag = memalloc_noreclaim_save();
+			else
+				memalloc_noreclaim_restore(noreclaim_flag);
+			__skb_queue_head_init(&sublist);
+		}
+		__skb_queue_tail(&sublist, skb);
+	}
+	/* Handle the last sublist */
+	__netif_receive_skb_list_core(&sublist, pfmemalloc);
+	/* Restore pflags */
+	if (pfmemalloc)
+		memalloc_noreclaim_restore(noreclaim_flag);
+}
+
 static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
 {
 	struct bpf_prog *old = rtnl_dereference(dev->xdp_prog);
@@ -4729,14 +4767,6 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
 	return ret;
 }
 
-static void __netif_receive_skb_list(struct sk_buff_head *list)
-{
-	struct sk_buff *skb;
-
-	while ((skb = __skb_dequeue(list)) != NULL)
-		__netif_receive_skb(skb);
-}
-
 static int netif_receive_skb_internal(struct sk_buff *skb)
 {
 	int ret;