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

[Roman Gushchin <guro@fb.com>]

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().

Thank you for working on it!

Roman