tuntap: reduce memory using of queues

A MAX_TAP_QUEUES(1024) queues of tuntap device is always allocated
unconditionally even userspace only requires a single queue device. This is
unnecessary and will lead a very high order of page allocation when has a high
possibility to fail. Solving this by creating a one queue net device when
userspace only use one queue and also reduce MAX_TAP_QUEUES to
DEFAULT_MAX_NUM_RSS_QUEUES which can guarantee the success of
the allocation.

Reported-by: Dirk Hohndel <dirk@hohndel.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 7 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index c81680dc10eb..8939d2117de2 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -109,11 +109,10 @@ struct tap_filter {
         unsigned char   addr[FLT_EXACT_COUNT][ETH_ALEN];
 };
 
-/* 1024 is probably a high enough limit: modern hypervisors seem to support on
- * the order of 100-200 CPUs so this leaves us some breathing space if we want
- * to match a queue per guest CPU.
- */
-#define MAX_TAP_QUEUES 1024
+/* DEFAULT_MAX_NUM_RSS_QUEUES were choosed to let the rx/tx queues allocated for
+ * the netdevice to be fit in one page. So we can make sure the success of
+ * memory allocation. TODO: increase the limit. */
+#define MAX_TAP_QUEUES DEFAULT_MAX_NUM_RSS_QUEUES
 
 #define TUN_FLOW_EXPIRE (3 * HZ)
 
@@ -1583,6 +1582,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
         else {
                 char *name;
                 unsigned long flags = 0;
+                int queues = ifr->ifr_flags & IFF_MULTI_QUEUE ?
+                             MAX_TAP_QUEUES : 1;
 
                 if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
                         return -EPERM;
@@ -1606,8 +1607,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                         name = ifr->ifr_name;
 
                 dev = alloc_netdev_mqs(sizeof(struct tun_struct), name,
-                                       tun_setup,
-                                       MAX_TAP_QUEUES, MAX_TAP_QUEUES);
+                                       tun_setup, queues, queues);
+
                 if (!dev)
                         return -ENOMEM;