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

[Salam Noureddine]

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 <nouredd...@arista.com>
---
 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
@@ -111,5 +111,6 @@ struct netns_ipv4 {
 #endif
 #endif
        atomic_t        rt_genid;
+       bool            needs_fib_flush;
 };
 #endif
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;
+       }
+
        in_dev = __in_dev_get_rtnl(dev);
        if (!in_dev)
                return NOTIFY_DONE;
@@ -1182,7 +1193,8 @@ static int fib_netdev_event(struct notifier_block *this, 
unsigned long event, vo
                rt_cache_flush(net);
                break;
        case NETDEV_DOWN:
-               fib_disable_ip(dev, event, false);
+               if (fib_sync_down_dev(dev, event, false))
+                       net->ipv4.needs_fib_flush = true;
                break;
        case NETDEV_CHANGE:
                flags = dev_get_flags(dev);
-- 
1.8.1.4