Re: [PATCH v2 net-next 4/4] net: fib: avoid calling fib_flush for each device when doing batch close and unregister

Call fib_flush at the end when closing or unregistering multiple
devices. This can save walking the fib many times and greatly
reduce rtnl_lock hold time when unregistering many devices with
a fib having hundreds of thousands of routes.

Signed-off-by: Salam Noureddine <redacted>
---
  include/net/netns/ipv4.h |  1 +
  net/ipv4/fib_frontend.c  | 16 ++++++++++++++--
  2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index d75be32..d59a078 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 4734475..808426e 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c

@@ -1161,11 +1161,22 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
  	unsigned int flags;

  	if (event == NETDEV_UNREGISTER) {
-		fib_disable_ip(dev, event, true);
+		if (fib_sync_down_dev(dev, event, true))
+			net->ipv4.needs_fib_flush = true;
  		rt_flush_dev(dev);
  		return NOTIFY_DONE;
  	}

+	if (event == NETDEV_UNREGISTER_BATCH || event == NETDEV_DOWN_BATCH) {
+		if (net->ipv4.needs_fib_flush) {
+			fib_flush(net);
+			net->ipv4.needs_fib_flush = false;
+		}
+		rt_cache_flush(net);
+		arp_ifdown_all();
+		return NOTIFY_DONE;
+	}
+