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Date:   Tue, 20 Jun 2023 18:13:18 +0800
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Subject: Re: Re: [PATCH net-next] inet: Save one atomic op if no memcg to
 charge
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To:     Eric Dumazet <edumazet@google.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "open list:NETWORKING [IPv4/IPv6]" <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20230619082547.73929-1-wuyun.abel@bytedance.com>
 <CANn89i+deprQWB0dmsUD1sRmy1VQCQwKnZUkLu_AEGV=ow=PKQ@mail.gmail.com>
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 <CANn89iK4hme4XmUyZVjTXMZYqAm8w+9tbwnrtHyJ3N28cAFYTw@mail.gmail.com>
From:   Abel Wu <wuyun.abel@bytedance.com>
In-Reply-To: <CANn89iK4hme4XmUyZVjTXMZYqAm8w+9tbwnrtHyJ3N28cAFYTw@mail.gmail.com>
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On 6/20/23 4:46 PM, Eric Dumazet wrote:
> On Tue, Jun 20, 2023 at 5:04 AM Abel Wu <wuyun.abel@bytedance.com> wrote:
>>
>> On 6/19/23 6:08 PM, Eric Dumazet wrote:
>>> On Mon, Jun 19, 2023 at 10:26 AM Abel Wu <wuyun.abel@bytedance.com> wrote:
>>>>
>>>> If there is no net-memcg associated with the sock, don't bother
>>>> calculating its memory usage for charge.
>>>>
>>>> Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
>>>> ---
>>>>    net/ipv4/inet_connection_sock.c | 18 +++++++++++-------
>>>>    1 file changed, 11 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
>>>> index 65ad4251f6fd..73798282c1ef 100644
>>>> --- a/net/ipv4/inet_connection_sock.c
>>>> +++ b/net/ipv4/inet_connection_sock.c
>>>> @@ -706,20 +706,24 @@ struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
>>>>    out:
>>>>           release_sock(sk);
>>>>           if (newsk && mem_cgroup_sockets_enabled) {
>>>> -               int amt;
>>>> +               int amt = 0;
>>>>
>>>>                   /* atomically get the memory usage, set and charge the
>>>>                    * newsk->sk_memcg.
>>>>                    */
>>>>                   lock_sock(newsk);
>>>>
>>>> -               /* The socket has not been accepted yet, no need to look at
>>>> -                * newsk->sk_wmem_queued.
>>>> -                */
>>>> -               amt = sk_mem_pages(newsk->sk_forward_alloc +
>>>> -                                  atomic_read(&newsk->sk_rmem_alloc));
>>>>                   mem_cgroup_sk_alloc(newsk);
>>>> -               if (newsk->sk_memcg && amt)
>>>> +               if (newsk->sk_memcg) {
>>>> +                       /* The socket has not been accepted yet, no need
>>>> +                        * to look at newsk->sk_wmem_queued.
>>>> +                        */
>>>> +                       amt = sk_mem_pages(newsk->sk_forward_alloc +
>>>> +                                          atomic_read(&newsk->sk_rmem_alloc));
>>>> +
>>>> +               }
>>>> +
>>>> +               if (amt)
>>>>                           mem_cgroup_charge_skmem(newsk->sk_memcg, amt,
>>>>                                                   GFP_KERNEL | __GFP_NOFAIL);
>>>
>>> This looks correct, but claiming reading an atomic_t is an 'atomic op'
>>> is a bit exaggerated.
>>
>> Yeah, shall I change subject to 'inet: Skip usage calculation if no
>> memcg to charge'? Or do you have any suggestions?
> 
> I would call this a cleanup or refactoring, maybe...

Alright, I have changed to 'cleanup', please take a look at v2.

Yet I have another question about this condition:
	'if (newsk && mem_cgroup_sockets_enabled)'
IMHO in the scope of cgroup v1, 'mem_cgroup_sockets_enabled' doesn't
imply socket accounting enabled for current's memcg. As the listening
socket and the newly accepted socket are processing same traffic, can
we make this condition more specific like this:
	'if (newsk && mem_cgroup_sockets_enabled && sk->sk_memcg)'
would you mind shedding some light please?

Thanks!
	Abel