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SubjectRe: Re: [PATCH net-next] inet: Save one atomic op if no memcg to charge
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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

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