Re: [PATCH v3] net: memcg: late association of sock to memcg

Shakeel Butt
2020-03-05T21:59:51Z

On Thu, Mar 5, 2020 at 1:17 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
>
>
> On 3/5/20 12:55 PM, 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 such 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>
> > ---
> > Changes since v2:
> > - Additional check for charging.
> > - Release the sock after charging.
> >
> > Changes since v1:
> > - added sk->sk_rmem_alloc to initial charging.
> > - added synchronization to get memory usage and set sk_memcg race-free.
> >
> > net/ipv4/inet_connection_sock.c | 20 ++++++++++++++++++++
> > 1 file changed, 20 insertions(+)
> >
> > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > index a4db79b1b643..5face55cf818 100644
> > --- a/net/ipv4/inet_connection_sock.c
> > +++ b/net/ipv4/inet_connection_sock.c
> > @@ -482,6 +482,26 @@ 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) {
> > + int amt;
> > +
> > + /* atomically get the memory usage, set and charge the
> > + * sk->sk_memcg.
> > + */
> > + lock_sock(newsk);
> > +
> > + /* The sk has not been accepted yet, no need to look at
> > + * sk->sk_wmem_queued.
> > + */
> > + amt = sk_mem_pages(newsk->sk_forward_alloc +
> > + atomic_read(&sk->sk_rmem_alloc));
> > + mem_cgroup_sk_alloc(newsk);
> > + if (newsk->sk_memcg && amt)
> > + mem_cgroup_charge_skmem(newsk->sk_memcg, amt);
> > +
> > + release_sock(newsk);
> > + }
> > out:
> > release_sock(sk);
> > if (req)
> >
>
> This patch looks fine, but why keeping the mem_cgroup_sk_alloc(newsk);
> in sk_clone_lock() ?
>
> Note that all TCP sk_clone_lock() calls happen in softirq context.

So, basically re-doing something like 9f1c2674b328 ("net: memcontrol:
defer call to mem_cgroup_sk_alloc()") in this patch. I am fine with
that.

Roman, any concerns?