netdev - Re: [PATCH net-next] kcm: do not attach sockets if sk_user

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Date:   Thu, 18 Jan 2018 11:46:33 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     James Chapman <jchapman@...alix.com>,
        Guillaume Nault <g.nault@...halink.fr>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] kcm: do not attach sockets if sk_user_data is
 already used

On Thu, 2018-01-18 at 11:26 -0800, Tom Herbert wrote:
> On Thu, Jan 18, 2018 at 10:08 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Thu, 2018-01-18 at 09:46 -0800, Tom Herbert wrote:
> > > 
> > > Then that's increasing the udp_sock structure size for a narrow use
> > > case which will get push back. I think it's going to be better to
> > > stick with one sock pointer. We could maybe redefine sk_user_data as a
> > > pointer to an allocated structure or array so it can hold multiple
> > > user_data pointers (in lieu of chaining).
> > > 
> > 
> > We do not have a lot of UDP sockets per host, I do not believe it
> > should be a problem adding stuff in them.
> > 
> 
> Eric,
> 
> Is QUIC using unconnected sockets then?

Server side is using a bunch of unconnected sockets, usually one per
cpu.

Note that UDP stack has no 4-tuple proper support yet, and even if it
had, extra memory costs would be huge on servers handling millions of
flows.