[VLAN]: Avoid a 4-order allocation.

This patch splits the vlan_group struct into a multi-allocated struct. On
x86_64, the size of the original struct is a little more than 32KB, causing
a 4-order allocation, which is prune to problems caused by buddy-system
external fragmentation conditions.

I couldn't just use vmalloc() because vfree() cannot be called in the
softirq context of the RCU callback.

Signed-off-by: Dan Aloni <da-x@monatomic.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 3 deletions

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 35cb3857358..d103580c72d 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -70,15 +70,34 @@ extern void vlan_ioctl_set(int (*hook)(void __user *));
  * depends on completely exhausting the VLAN identifier space.  Thus
  * it gives constant time look-up, but in many cases it wastes memory.
  */
-#define VLAN_GROUP_ARRAY_LEN 4096
+#define VLAN_GROUP_ARRAY_LEN          4096
+#define VLAN_GROUP_ARRAY_SPLIT_PARTS  8
+#define VLAN_GROUP_ARRAY_PART_LEN     (VLAN_GROUP_ARRAY_LEN/VLAN_GROUP_ARRAY_SPLIT_PARTS)
 
 struct vlan_group {
 	int real_dev_ifindex; /* The ifindex of the ethernet(like) device the vlan is attached to. */
 	struct hlist_node	hlist;	/* linked list */
-	struct net_device *vlan_devices[VLAN_GROUP_ARRAY_LEN];
+	struct net_device **vlan_devices_arrays[VLAN_GROUP_ARRAY_SPLIT_PARTS];
 	struct rcu_head		rcu;
 };
 
+static inline struct net_device *vlan_group_get_device(struct vlan_group *vg, int vlan_id)
+{
+	struct net_device **array;
+	array = vg->vlan_devices_arrays[vlan_id / VLAN_GROUP_ARRAY_PART_LEN];
+	return array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN];
+}
+
+static inline void vlan_group_set_device(struct vlan_group *vg, int vlan_id,
+					 struct net_device *dev)
+{
+	struct net_device **array;
+	if (!vg)
+		return;
+	array = vg->vlan_devices_arrays[vlan_id / VLAN_GROUP_ARRAY_PART_LEN];
+	array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] = dev;
+}
+
 struct vlan_priority_tci_mapping {
 	unsigned long priority;
 	unsigned short vlan_qos; /* This should be shifted when first set, so we only do it
@@ -160,7 +179,7 @@ static inline int __vlan_hwaccel_rx(struct sk_buff *skb,
 		return NET_RX_DROP;
 	}
 
-	skb->dev = grp->vlan_devices[vlan_tag & VLAN_VID_MASK];
+	skb->dev = vlan_group_get_device(grp, vlan_tag & VLAN_VID_MASK);
 	if (skb->dev == NULL) {
 		dev_kfree_skb_any(skb);