Re: [PATCH] net: memcg: late association of sock to memcg

[Shakeel Butt <shakeelb@google.com>]

On Sun, Feb 23, 2020 at 11:29 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Fri, Feb 21, 2020 at 5:05 PM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > If a TCP socket is allocated in IRQ context or cloned from unassociated
> > (i.e. not associated to a memcg) in IRQ context then it will remain
> > unassociated for its whole life. Almost half of the TCPs created on the
> > system are created in IRQ context, so, memory used by suck sockets will
> > not be accounted by the memcg.
> >
> > This issue is more widespread in cgroup v1 where network memory
> > accounting is opt-in but it can happen in cgroup v2 if the source socket
> > for the cloning was created in root memcg.
> >
> > To fix the issue, just do the late association of the unassociated
> > sockets at accept() time in the process context and then force charge
> > the memory buffer already reserved by the socket.
> >
> > Signed-off-by: Shakeel Butt <shakeelb@google.com>
> > ---
> >  net/ipv4/inet_connection_sock.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > index a4db79b1b643..df9c8ef024a2 100644
> > --- a/net/ipv4/inet_connection_sock.c
> > +++ b/net/ipv4/inet_connection_sock.c
> > @@ -482,6 +482,13 @@ struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
> >                 }
> >                 spin_unlock_bh(&queue->fastopenq.lock);
> >         }
> > +
> > +       if (mem_cgroup_sockets_enabled && !newsk->sk_memcg) {
> > +               mem_cgroup_sk_alloc(newsk);
> > +               if (newsk->sk_memcg)
> > +                       mem_cgroup_charge_skmem(newsk->sk_memcg,
> > +                                       sk_mem_pages(newsk->sk_forward_alloc));
>
> I am not sure what you  are trying to do here.
>
> sk->sk_forward_alloc is not the total amount of memory used by a TCP socket.
> It is only some part that has been reserved, but not yet consumed.
>
> For example, every skb that has been stored in TCP receive queue or
> out-of-order queue might have
> used memory.
>
> I guess that if we assume that  a not yet accepted socket can not have
> any outstanding data in its transmit queue,
> you need to use sk->sk_rmem_alloc as well.

Thanks a lot. I will add that with a comment. BTW for my knowledge
which field represents the transmit queue size?

>
> To test this patch, make sure to add a delay before accept(), so that
> 2MB worth of data can be queued before accept() happens.

Yes, I will test this with a delay.

thanks,
Shakeel