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From:   Yafang Shao <laoar.shao@gmail.com>
Date:   Sat, 30 Jun 2018 18:53:36 +0800
Message-ID: <CALOAHbAXXB=WfG_ibcdbuNPRu8KDUPWurgaEU2yuBBSh386V1w@mail.gmail.com>
Subject: Re: [PATCH net-next] net, mm: avoid unnecessary memcg charge skmem
To:     David Miller <davem@davemloft.net>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Yafang Shao <laoar.shao@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Sat, Jun 30, 2018 at 6:09 PM, Yafang Shao <laoar.shao@gmail.com> wrote:
> In __sk_mem_raise_allocated(), if mem_cgroup_charge_skmem() return
> false, mem_cgroup_uncharge_skmem will be executed.
>
> The logic is as bellow,
> __sk_mem_raise_allocated
>         ret = mem_cgroup_uncharge_skmem
>                 try_charge(memcg, gfp_mask|__GFP_NOFAIL, nr_pages);
>                 return false
>         if (!ret)
>                 mem_cgroup_uncharge_skmem(sk->sk_memcg, amt);
>
> So it is unnecessary to charge if it is not forced.
>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  include/linux/memcontrol.h |  3 ++-
>  mm/memcontrol.c            | 12 +++++++++---
>  net/core/sock.c            |  5 +++--
>  net/ipv4/tcp_output.c      |  2 +-
>  4 files changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 6c6fb11..56c07c9 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1160,7 +1160,8 @@ static inline void mem_cgroup_wb_stats(struct bdi_writeback *wb,
>  #endif /* CONFIG_CGROUP_WRITEBACK */
>
>  struct sock;
> -bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages);
> +bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
> +                            bool force);
>  void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages);
>  #ifdef CONFIG_MEMCG
>  extern struct static_key_false memcg_sockets_enabled_key;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e6f0d5e..1122be2 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5929,7 +5929,8 @@ void mem_cgroup_sk_free(struct sock *sk)
>   * Charges @nr_pages to @memcg. Returns %true if the charge fit within
>   * @memcg's configured limit, %false if the charge had to be forced.
>   */
> -bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
> +bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
> +                            bool force)
>  {
>         gfp_t gfp_mask = GFP_KERNEL;
>
> @@ -5940,7 +5941,10 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
>                         memcg->tcpmem_pressure = 0;
>                         return true;
>                 }
> -               page_counter_charge(&memcg->tcpmem, nr_pages);
> +
> +               if (force)
> +                       page_counter_charge(&memcg->tcpmem, nr_pages);
> +
>                 memcg->tcpmem_pressure = 1;
>                 return false;
>         }
> @@ -5954,7 +5958,9 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
>         if (try_charge(memcg, gfp_mask, nr_pages) == 0)
>                 return true;
>
> -       try_charge(memcg, gfp_mask|__GFP_NOFAIL, nr_pages);
> +       if (force)
> +               try_charge(memcg, gfp_mask|__GFP_NOFAIL, nr_pages);
> +
>         return false;
>  }
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index bcc4182..148a840 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2401,9 +2401,10 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
>  {
>         struct proto *prot = sk->sk_prot;
>         long allocated = sk_memory_allocated_add(sk, amt);
> +       bool charged = false;
>
>         if (mem_cgroup_sockets_enabled && sk->sk_memcg &&
> -           !mem_cgroup_charge_skmem(sk->sk_memcg, amt))
> +           !(charged = mem_cgroup_charge_skmem(sk->sk_memcg, amt, false)))
>                 goto suppress_allocation;
>
>         /* Under limit. */
> @@ -2465,7 +2466,7 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
>
>         sk_memory_allocated_sub(sk, amt);
>
> -       if (mem_cgroup_sockets_enabled && sk->sk_memcg)
> +       if (mem_cgroup_sockets_enabled && sk->sk_memcg && charged)
>                 mem_cgroup_uncharge_skmem(sk->sk_memcg, amt);
>
>         return 0;
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index f8f6129..9b741d4 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3014,7 +3014,7 @@ void sk_forced_mem_schedule(struct sock *sk, int size)
>         sk_memory_allocated_add(sk, amt);
>
>         if (mem_cgroup_sockets_enabled && sk->sk_memcg)
> -               mem_cgroup_charge_skmem(sk->sk_memcg, amt);
> +               mem_cgroup_charge_skmem(sk->sk_memcg, amt, true);
>  }
>
>  /* Send a FIN. The caller locks the socket for us.
> --
> 1.8.3.1
>

Pls. ignore this patch.

Sorry about the noise.

Thanks
Yafang