netdev - Re: [PATCHv2 net-next 2/2] ipv4/fib: send notify when delete source address routes

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Date: Mon, 11 Sep 2023 11:35:05 +0200
From: Thomas Haller <thaller@...hat.com>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Ido Schimmel
 <idosch@...dia.com>,  David Ahern <dsahern@...nel.org>, Benjamin Poirier
 <bpoirier@...dia.com>, Stephen Hemminger <stephen@...workplumber.org>, Eric
 Dumazet <edumazet@...gle.com>
Subject: Re: [PATCHv2 net-next 2/2] ipv4/fib: send notify when delete source
 address routes

On Mon, 2023-08-28 at 14:14 +0800, Hangbin Liu wrote:
> > > 
> > > In the other thread Thomas mentioned that NM already requests a
> > > route
> > > dump following address deletion [1]. If so, can Thomas or you
> > > please
> > > explain how this patch is going to help NM? Is the intention to
> > > optimize
> > > things and avoid the dump request (which can only work on new
> > > kernels)?
> > > 
> > > [1]
> > > https://lore.kernel.org/netdev/07fcfd504148b3c721fda716ad0a549662708407.camel@redhat.com/
> > 
> > In my understanding, After deleting an address, deal with the
> > delete notify is
> > more efficient to maintain the route cache than dump all the
> > routes.

Hi,

NetworkManager does so out of necessity, as there is no notification.
Overall, it seems a pretty bad thing to do, because it's expensive if
you have many routes/addresses.

Unfortunately, it's hard to ever drop a workaround, because we never
know when the workaround can be dropped.

Also, it's simply a notification missing, and not tied to
NetworkManager or to maintaining a cache. If you run `ip route
monitor`, you also don't see the notification that kernel drops a
route? The effort that NetworkManager takes to maintain correct
information is not something that most programs would do.

Thomas