[RFC 3/4] tuntap: reduce the size of tun_struct by using flex array

Pankaj Gupta
2014-08-18T13:38:50Z

This patch switches to flex array to implement the flow caches, it brings
several advantages:

- Reduce the size of the tun_struct structure, which allows us to increase the
upper limit of queues in future.
- Avoid higher order memory allocation. It will be useful when switching to
pure hashing in flow cache which may demand a larger size array in future.

After this patch, the size of tun_struct on x86_64 reduced from 8512 to
328

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
---
drivers/net/tun.c | 49 +++++++++++++++++++++++++++++++++++++------------
1 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index acaaf67..7dd495f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -65,6 +65,7 @@
#include <linux/nsproxy.h>
#include <linux/virtio_net.h>
#include <linux/rcupdate.h>
+#include <linux/flex_array.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/rtnetlink.h>
@@ -186,7 +187,7 @@ struct tun_struct {
int debug;
#endif
spinlock_t lock;
- struct hlist_head flows[TUN_NUM_FLOW_ENTRIES];
+ struct flex_array *flows;
struct timer_list flow_gc_timer;
unsigned long ageing_time;
unsigned int numdisabled;
@@ -247,10 +248,11 @@ static void tun_flow_flush(struct tun_struct *tun)

spin_lock_bh(&tun->lock);
for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
+ struct hlist_head *h = flex_array_get(tun->flows, i);
struct tun_flow_entry *e;
struct hlist_node *n;

- hlist_for_each_entry_safe(e, n, &tun->flows[i], hash_link)
+ hlist_for_each_entry_safe(e, n, h, hash_link)
tun_flow_delete(tun, e);
}
spin_unlock_bh(&tun->lock);
@@ -262,10 +264,11 @@ static void tun_flow_delete_by_queue(struct tun_struct *tun, u16 queue_index)

spin_lock_bh(&tun->lock);
for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
+ struct hlist_head *h = flex_array_get(tun->flows, i);
struct tun_flow_entry *e;
struct hlist_node *n;

- hlist_for_each_entry_safe(e, n, &tun->flows[i], hash_link) {
+ hlist_for_each_entry_safe(e, n, h, hash_link) {
if (e->queue_index == queue_index)
tun_flow_delete(tun, e);
}
@@ -285,10 +288,11 @@ static void tun_flow_cleanup(unsigned long data)

spin_lock_bh(&tun->lock);
for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++) {
+ struct hlist_head *h = flex_array_get(tun->flows, i);
struct tun_flow_entry *e;
struct hlist_node *n;

- hlist_for_each_entry_safe(e, n, &tun->flows[i], hash_link) {
+ hlist_for_each_entry_safe(e, n, h, hash_link) {
unsigned long this_timer;
count++;
this_timer = e->updated + delay;
@@ -315,7 +319,7 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
if (!rxhash)
return;
else
- head = &tun->flows[tun_hashfn(rxhash)];
+ head = flex_array_get(tun->flows, tun_hashfn(rxhash));

rcu_read_lock();

@@ -378,7 +382,8 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,

txq = skb_get_hash(skb);
if (txq) {
- e = tun_flow_find(&tun->flows[tun_hashfn(txq)], txq);
+ e = tun_flow_find(flex_array_get(tun->flows,
+ tun_hashfn(txq)), txq);
if (e) {
tun_flow_save_rps_rxhash(e, txq);
txq = e->queue_index;
@@ -758,8 +763,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
rxhash = skb_get_hash(skb);
if (rxhash) {
struct tun_flow_entry *e;
- e = tun_flow_find(&tun->flows[tun_hashfn(rxhash)],
- rxhash);
+ e = tun_flow_find(flex_array_get(tun->flows,
+ tun_hashfn(rxhash)), rxhash);
if (e)
tun_flow_save_rps_rxhash(e, rxhash);
}
@@ -894,23 +899,40 @@ static const struct net_device_ops tap_netdev_ops = {
#endif
};

-static void tun_flow_init(struct tun_struct *tun)
+static int tun_flow_init(struct tun_struct *tun)
{
- int i;
+ struct flex_array *buckets;
+ int i, err;
+
+ buckets = flex_array_alloc(sizeof(struct hlist_head),
+ TUN_NUM_FLOW_ENTRIES, GFP_KERNEL);
+ if (!buckets)
+ return -ENOMEM;
+
+ err = flex_array_prealloc(buckets, 0, TUN_NUM_FLOW_ENTRIES, GFP_KERNEL);
+ if (err) {
+ flex_array_free(buckets);
+ return -ENOMEM;
+ }

+ tun->flows = buckets;
for (i = 0; i < TUN_NUM_FLOW_ENTRIES; i++)
- INIT_HLIST_HEAD(&tun->flows[i]);
+ INIT_HLIST_HEAD((struct hlist_head *)
+ flex_array_get(buckets, i));

tun->ageing_time = TUN_FLOW_EXPIRE;
setup_timer(&tun->flow_gc_timer, tun_flow_cleanup, (unsigned long)tun);
mod_timer(&tun->flow_gc_timer,
round_jiffies_up(jiffies + tun->ageing_time));
+
+ return 0;
}

static void tun_flow_uninit(struct tun_struct *tun)
{
del_timer_sync(&tun->flow_gc_timer);
tun_flow_flush(tun);
+ flex_array_free(tun->flows);
}

/* Initialize net device. */
@@ -1659,7 +1681,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
goto err_free_dev;

tun_net_init(dev);
- tun_flow_init(tun);
+
+ err = tun_flow_init(tun);
+ if (err < 0)
+ goto err_free_dev;

dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
--
1.7.1