[RFC net-next] ipv4: Don't promote secondaries when flushing addresses

[Jakub Sitnicki <jkbs@redhat.com>]

Promoting secondary addresses on address removal makes flushing all
addresses from a device with 1000's of them slow. This is because we
cannot take down the secondary addresses when we are removing the
primary one, which would make it faster.

However, the userspace, when performing a flush, will in the end remove
all the addresses regardless of secondary address promotion taking
place. Unfortunately the kernel currently cannot distinguish between a
single address removal and a flush of all addresses.

To help with this case introduce a IFA_F_FLUSH flag that can be used by
userspace to signal that a removal operation is being done because of a
flush. When the flag is set, don't bother with secondary address
promotion as we expect that secondary addresses will be removed soon as
well.

Signed-off-by: Jakub Sitnicki <jkbs@redhat.com>

---

A benchmark involving a flush of 40,000 addresses from a dummy device
shows a x4 speed-up of the 'flush' operation. 'ip' had to be modified to
set the IFA_F_FLUSH flag for RTM_DELADDR requests issued for the
'flush':

  # time $IP -stats addr flush dev dum0

Before:

  real    0m30.596s
  user    0m0.000s
  sys     0m30.567s

After:

  real    0m7.601s
  user    0m0.000s
  sys     0m7.569s

It's also worth noting that promote_secondaries sysctl param is enabled by
default since systemd 216 thus making it the new "normal" on some distros.


 include/uapi/linux/if_addr.h |  1 +
 net/ipv4/devinet.c           | 14 ++++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/if_addr.h b/include/uapi/linux/if_addr.h
index ebaf5701c9db..19aab9a9cec5 100644
--- a/include/uapi/linux/if_addr.h
+++ b/include/uapi/linux/if_addr.h
@@ -54,6 +54,7 @@ enum {
 #define IFA_F_NOPREFIXROUTE	0x200
 #define IFA_F_MCAUTOJOIN	0x400
 #define IFA_F_STABLE_PRIVACY	0x800
+#define IFA_F_FLUSH		0x1000

 struct ifa_cacheinfo {
 	__u32	ifa_prefered;
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index d7585ab1a77a..1f436e1e5222 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -331,13 +331,14 @@ int inet_addr_onlink(struct in_device *in_dev, __be32 a, __be32 b)
 }

 static void __inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
-			 int destroy, struct nlmsghdr *nlh, u32 portid)
+			   int destroy, struct nlmsghdr *nlh, u32 portid,
+			   bool flush)
 {
 	struct in_ifaddr *promote = NULL;
 	struct in_ifaddr *ifa, *ifa1 = *ifap;
 	struct in_ifaddr *last_prim = in_dev->ifa_list;
 	struct in_ifaddr *prev_prom = NULL;
-	int do_promote = IN_DEV_PROMOTE_SECONDARIES(in_dev);
+	int do_promote = IN_DEV_PROMOTE_SECONDARIES(in_dev) && !flush;

 	ASSERT_RTNL();

@@ -437,7 +438,7 @@ static void __inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
 static void inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
 			 int destroy)
 {
-	__inet_del_ifa(in_dev, ifap, destroy, NULL, 0);
+	__inet_del_ifa(in_dev, ifap, destroy, NULL, 0, false);
 }

 static void check_lifetime(struct work_struct *work);
@@ -607,6 +608,7 @@ static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh,
 	struct in_device *in_dev;
 	struct ifaddrmsg *ifm;
 	struct in_ifaddr *ifa, **ifap;
+	bool flush = false;
 	int err = -EINVAL;

 	ASSERT_RTNL();
@@ -623,6 +625,9 @@ static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh,
 		goto errout;
 	}

+	if (tb[IFA_FLAGS])
+		flush = !!(nla_get_u32(tb[IFA_FLAGS]) & IFA_F_FLUSH);
+
 	for (ifap = &in_dev->ifa_list; (ifa = *ifap) != NULL;
 	     ifap = &ifa->ifa_next) {
 		if (tb[IFA_LOCAL] &&
@@ -639,7 +644,8 @@ static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh,

 		if (ipv4_is_multicast(ifa->ifa_address))
 			ip_mc_config(net->ipv4.mc_autojoin_sk, false, ifa);
-		__inet_del_ifa(in_dev, ifap, 1, nlh, NETLINK_CB(skb).portid);
+		__inet_del_ifa(in_dev, ifap, 1, nlh, NETLINK_CB(skb).portid,
+			       flush);
 		return 0;
 	}