Re: RFC: Should net namespaces scale up (>10k) ?

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Johannes Berg <johannes@sipsolutions.net>
Date: Tue, 08 Oct 2024 20:22:38 +0200
> On Tue, 2024-10-08 at 10:47 -0700, Kuniyuki Iwashima wrote:
> 
> > > 1. The "netdevice notifier" from the Wireless Extensions subsystem
> > > insists on scanning the whole list regardless of the nature of the
> > > change, nor wondering whether all these namespaces hold any wireless
> > > interface, nor even whether the system has _any_ wireless hardware...
> > > 
> > >         for_each_net(net) {
> > >                 while ((skb = skb_dequeue(&net->wext_nlevents)))
> > >                         rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL,
> > >                                     GFP_KERNEL);
> > >         }
> > > 
> > 
> > Alex forwarded this mail to me and asked about 1.
> > 
> > I checked 8bf862739a778, but I didn't see why wext_netdev_notifier_call()
> > needs to iterate all netns.
> 
> Agree. That code is ancient, and I don't remember why, but I'd think
> it's just because I was lazy then.
> 
> > diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> > index 838ad6541a17..d4b613fc650c 100644
> > --- a/net/wireless/wext-core.c
> > +++ b/net/wireless/wext-core.c
> > @@ -343,17 +343,22 @@ static const int compat_event_type_size[] = {
> >  
> >  /* IW event code */
> >  
> > -void wireless_nlevent_flush(void)
> > +static void wireless_nlevent_flush_net(struct net *net)
> >  {
> >  	struct sk_buff *skb;
> > +
> > +	while ((skb = skb_dequeue(&net->wext_nlevents)))
> > +		rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL,
> > +			    GFP_KERNEL);
> > +}
> > +
> > +void wireless_nlevent_flush(void)
> > +{
> >  	struct net *net;
> >  
> >  	down_read(&net_rwsem);
> > -	for_each_net(net) {
> > -		while ((skb = skb_dequeue(&net->wext_nlevents)))
> > -			rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL,
> > -				    GFP_KERNEL);
> > -	}
> > +	for_each_net(net)
> > +		wireless_nlevent_flush_net(net);
> >  	up_read(&net_rwsem);
> >  }
> >  EXPORT_SYMBOL_GPL(wireless_nlevent_flush);
> 
> Note 1: I just posted this patch yesterday:
> https://lore.kernel.org/linux-wireless/20241007214715.3dd736dc3ac0.I1388536e99c37f28a007dd753c473ad21513d9a9@changeid/
> 
> so that would conflict here, I'd think.
> 
> Note 2: the only other caller to wireless_nlevent_flush() is from
> wireless_nlevent_process()/wireless_nlevent_work, and that work could
> easily be made per netns since it comes along with net->wext_nlevents,
> and then we don't need any global function at all. Seems this could be
> implemented in wext_pernet_init()/wext_pernet_exit() pretty easily?

Sounds good.

I'll post a patch after yours lands on wireless-next.

Thanks!