netdev - Re: [PATCH net-next v3 2/3] udp: implement memory accounting helpers

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Date:   Thu, 29 Sep 2016 16:34:40 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     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>,
        Edward Cree <ecree@...arflare.com>, linux-nfs@...r.kernel.org
Subject: Re: [PATCH net-next v3 2/3] udp: implement memory accounting helpers

On Thu, 2016-09-29 at 07:13 -0700, Eric Dumazet wrote:
> On Thu, 2016-09-29 at 16:01 +0200, Paolo Abeni wrote:
> 
> > When we reach __sk_mem_reduce_allocated() we are sure we can free the
> > specified amount of memory, so we only need to ensure consistent
> > sk_prot->memory_allocated updates. The current atomic operation suffices
> > to this.
> 
> Then why are you updating sk->sk_forward_alloc using racy operations ?
> 
> If this is not needed or racy, do not do it.

Thank you for all the feedback.

The actual forward allocated memory value is:

atomic_read(&up->mem_allocated) - atomic_read(&sk->sk_rmem_alloc).

sk_forward_alloc is updated only to hint to the user space the forward
allocated memory value via the diag interface.

If such information is not needed we can drop the update, and
sk_forward_alloc will always be seen as 0 even when the socket has some
forward allocation.

Cheers,

Paolo