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

[Shakeel Butt <shakeelb@google.com>]

On Fri, Feb 21, 2020 at 5:49 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Fri, Feb 21, 2020 at 05:04:56PM -0800, Shakeel Butt 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>
>
> Hello, Shakeel!
>
> > ---
> >  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));
> > +     }
>
> Looks good for me from the memcg side. Let's see what networking people will say...
>
> Btw, do you plan to make a separate patch for associating the socket with the default
> cgroup on the unified hierarchy? I mean cgroup_sk_alloc().
>

Yes. I tried to do that here but was not able to do without adding the
(newsk->sk_cgrp_data.val) check which I can not do in this file as
sk_cgrp_data might not be compiled. I will send a separate patch.

Shakeel