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

[Eric Dumazet]

On Tue, Jun 20, 2023 at 5:04 AM Abel Wu <wuyun.abel@xxxxxxxxxxxxx> wrote:
>
> On 6/19/23 6:08 PM, Eric Dumazet wrote:
> > On Mon, Jun 19, 2023 at 10:26 AM Abel Wu <wuyun.abel@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> >> ---
> >>   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...