From: Christoph Paasch Date: Sat, 16 Aug 2025 23:12:49 +0000 (-0700) Subject: net: When removing nexthops, don't call synchronize_net if it is not necessary X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=b0ac6d3b56a2384db151696cfda2836a8a961b6d;p=users%2Fwilly%2Flinux.git net: When removing nexthops, don't call synchronize_net if it is not necessary When removing a nexthop, commit 90f33bffa382 ("nexthops: don't modify published nexthop groups") added a call to synchronize_rcu() (later changed to _net()) to make sure everyone sees the new nexthop-group before the rtnl-lock is released. When one wants to delete a large number of groups and nexthops, it is fastest to first flush the groups (ip nexthop flush groups) and then flush the nexthops themselves (ip -6 nexthop flush). As that way the groups don't need to be rebalanced. However, `ip -6 nexthop flush` will still take a long time if there is a very large number of nexthops because of the call to synchronize_net(). Now, if there are no more groups, there is no point in calling synchronize_net(). So, let's skip that entirely by checking if nh->grp_list is empty. This gives us a nice speedup: BEFORE: ======= $ time sudo ip -6 nexthop flush Dump was interrupted and may be inconsistent. Flushed 2097152 nexthops real 1m45.345s user 0m0.001s sys 0m0.005s $ time sudo ip -6 nexthop flush Dump was interrupted and may be inconsistent. Flushed 4194304 nexthops real 3m10.430s user 0m0.002s sys 0m0.004s AFTER: ====== $ time sudo ip -6 nexthop flush Dump was interrupted and may be inconsistent. Flushed 2097152 nexthops real 0m17.545s user 0m0.003s sys 0m0.003s $ time sudo ip -6 nexthop flush Dump was interrupted and may be inconsistent. Flushed 4194304 nexthops real 0m35.823s user 0m0.002s sys 0m0.004s Signed-off-by: Christoph Paasch Reviewed-by: Ido Schimmel Reviewed-by: Nikolay Aleksandrov Reviewed-by: Eric Dumazet Reviewed-by: David Ahern Link: https://patch.msgid.link/20250816-nexthop_dump-v2-2-491da3462118@openai.com Signed-off-by: Jakub Kicinski --- diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index 509004bfd08e..0a20625f5ffb 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -2087,6 +2087,12 @@ static void remove_nexthop_from_groups(struct net *net, struct nexthop *nh, { struct nh_grp_entry *nhge, *tmp; + /* If there is nothing to do, let's avoid the costly call to + * synchronize_net() + */ + if (list_empty(&nh->grp_list)) + return; + list_for_each_entry_safe(nhge, tmp, &nh->grp_list, nh_list) remove_nh_grp_entry(net, nhge, nlinfo);