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

[Abel Wu]

On 6/20/23 4:46 PM, Eric Dumazet wrote:
> 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...

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