[VLAN]: Reduce memory consumed by vlan_groups

Currently each vlan_groupd contains 8 pointers on arrays with 512
pointers on struct net_device each  :)  Such a construction "in many
cases ... wastes memory".

My proposal is to allow for some of these arrays pointers be NULL,
meaning that there are no devices in it. When a new device is added
to the vlan_group, the appropriate array is allocated.

The check in vlan_group_get_device's is safe, since the pointer
vg->vlan_devices_arrays[x] can only switch from NULL to not-NULL.
The vlan_group_prealloc_vid() is guarded with rtnl lock and is
also safe.

I've checked (I hope that) all the places, that use these arrays
and found, that the register_vlan_dev is the only place, that can
put a vlan device on an empty vlan_group.

Rough calculations shows, that after the patch a setup with a
single vlan dev (or up to 512 vlans with sequential vids) will
occupy approximately 8 times less memory.

The question I have is - does this patch makes sense, or a totally
new structures are required to store the vlan_devs?

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 23 insertions, 13 deletions

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index c35dc230365c..694be86e4490 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -106,29 +106,35 @@ static void vlan_group_free(struct vlan_group *grp)
 static struct vlan_group *vlan_group_alloc(int ifindex)
 {
         struct vlan_group *grp;
-        unsigned int size;
-        unsigned int i;
 
         grp = kzalloc(sizeof(struct vlan_group), GFP_KERNEL);
         if (!grp)
                 return NULL;
 
-        size = sizeof(struct net_device *) * VLAN_GROUP_ARRAY_PART_LEN;
-
-        for (i = 0; i < VLAN_GROUP_ARRAY_SPLIT_PARTS; i++) {
-                grp->vlan_devices_arrays[i] = kzalloc(size, GFP_KERNEL);
-                if (!grp->vlan_devices_arrays[i])
-                        goto err;
-        }
-
         grp->real_dev_ifindex = ifindex;
         hlist_add_head_rcu(&grp->hlist,
                            &vlan_group_hash[vlan_grp_hashfn(ifindex)]);
         return grp;
+}
 
-err:
-        vlan_group_free(grp);
-        return NULL;
+static int vlan_group_prealloc_vid(struct vlan_group *vg, int vid)
+{
+        struct net_device **array;
+        unsigned int size;
+
+        ASSERT_RTNL();
+
+        array = vg->vlan_devices_arrays[vid / VLAN_GROUP_ARRAY_PART_LEN];
+        if (array != NULL)
+                return 0;
+
+        size = sizeof(struct net_device *) * VLAN_GROUP_ARRAY_PART_LEN;
+        array = kzalloc(size, GFP_KERNEL);
+        if (array == NULL)
+                return -ENOBUFS;
+
+        vg->vlan_devices_arrays[vid / VLAN_GROUP_ARRAY_PART_LEN] = array;
+        return 0;
 }
 
 static void vlan_rcu_free(struct rcu_head *rcu)
@@ -247,6 +253,10 @@ int register_vlan_dev(struct net_device *dev)
                         return -ENOBUFS;
         }
 
+        err = vlan_group_prealloc_vid(grp, vlan_id);
+        if (err < 0)
+                goto out_free_group;
+
         err = register_netdevice(dev);
         if (err < 0)
                 goto out_free_group;