netdev - Re: [PATCH net-next 2/3] udp: implement memory accounting helpers

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Date:   Thu, 22 Sep 2016 13:37:21 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Edward Cree <ecree@...arflare.com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        James Morris <jmorris@...ei.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Alexander Duyck <aduyck@...antis.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Tom Herbert <tom@...bertland.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        linux-nfs@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] udp: implement memory accounting helpers

On Thu, 2016-09-22 at 13:34 -0700, Eric Dumazet wrote:
> On Thu, 2016-09-22 at 22:27 +0200, Paolo Abeni wrote:
> > On Thu, 2016-09-22 at 09:30 -0700, Eric Dumazet wrote:
> > > On Thu, 2016-09-22 at 18:14 +0200, Paolo Abeni wrote:
> > > 
> > > > I think that the idea behind using atomic ops directly on
> > > > sk_forward_alloc is to avoid adding other fields to the udp_socket. 
> > > > 
> > > > If we can add some fields to the udp_sock structure, the schema proposed
> > > > in this patch should fit better (modulo bugs ;-), always requiring a
> > > > single atomic operation at memory reclaiming time and at memory
> > > > allocation time.
> > > 
> > > But do we want any additional atomic to begin with ?
> > > 
> > > Given typical number of UDP sockets on a host, we could reserve/forward
> > > alloc at socket creation time, and when SO_RCVBUF is changed.
> > 
> > That would be very efficient and would probably work on most scenario,
> > but if/when the system will reach udp memory pressure things will be
> > very bad: forward allocation on open() will fail and nobody will be able
> > to create any new udp socket, right ?
> > 
> 
> No, we could allow one page per socket (udp_mem[0]) and applications
> would still work.

I meant udp_rmem_min, not udp_mem[0]

udp_rmem_min - INTEGER
        Minimal size of receive buffer used by UDP sockets in moderation.
        Each UDP socket is able to use the size for receiving data, even if
        total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
        Default: 1 page