netdev - Re: [PATCH net-next 3/3] ipv6: obsolete cached dst when removing them from fib tree

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Date:   Wed, 18 Oct 2017 22:30:29 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Martin KaFai Lau <kafai@...com>, Wei Wang <weiwan@...gle.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Xin Long <lucien.xin@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net-next 3/3] ipv6: obsolete cached dst when removing
 them from fib tree

On Wed, 2017-10-18 at 12:05 -0700, Martin KaFai Lau wrote:
> Another thing (not limited to this case),
> 
> Considering we have a limited size in the exception table now and
> the oldest one will get removed when the table is full,
> do we still need to purge this periodically in gc?

At least in some scenarios we have only a few entries in the exception
table.

> I would like to see the IPv6's gc eventually goes away.
> 
> If we need to expire the pmtu value of a RTF_CACHE rt,
> can dst.expires be checked during the lookup (like what
> ipv4 is doing) and then remove it from the exception table?

Currently the gc also performs validation vs the related neigh for
GATEWAY dst. That looks potentially quite expensive, as we currently
have a per neighbour atomic refcount (e.g. if the same dst is cached on
different CPUs)

Cheers,

Paolo