5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Christoph Paasch cpaasch@openai.com
[ Upstream commit b0ac6d3b56a2384db151696cfda2836a8a961b6d ]
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 cpaasch@openai.com Reviewed-by: Ido Schimmel idosch@nvidia.com Reviewed-by: Nikolay Aleksandrov razor@blackwall.org Reviewed-by: Eric Dumazet edumazet@google.com Reviewed-by: David Ahern dsahern@kernel.org Link: https://patch.msgid.link/20250816-nexthop_dump-v2-2-491da3462118@openai.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/nexthop.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index 388f5773b88d2..3a807ae69a12e 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -760,6 +760,12 @@ 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);