Re: [PATCH net-next v2 2/2] net: When removing nexthops, don't call synchronize_net if it is not necessary

[Ido Schimmel <idosch@idosch.org>]

On Sat, Aug 16, 2025 at 04:12:49PM -0700, Christoph Paasch via B4 Relay wrote:
> From: Christoph Paasch <cpaasch@openai.com>
> 
> 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.

[...]

> Signed-off-by: Christoph Paasch <cpaasch@openai.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>