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Commit 67727184 authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by David S. Miller
Browse files

[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: default avatarPavel Emelyanov <xemul@openvz.org>
Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
parent 789e41e6

include/linux/if_vlan.h

+1 −1
Original line number Diff line number Diff line
@@ -93,7 +93,7 @@ static inline struct net_device *vlan_group_get_device(struct vlan_group *vg, 
{

	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];

	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL;

}



static inline void vlan_group_set_device(struct vlan_group *vg,

net/8021q/vlan.c

+23 −13
Original line number Diff line number Diff line
@@ -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;