linux-kernel - Re: [PATCH next-20130703] net: sock: Add ifdef CONFIG_MEMCG_KMEM for mem_cgroup_sockets

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Message-ID: <CA+icZUV0bCUDxd8qtzS-zNGwM+JKEqC4uTCxmsOH8jbNVddPXA@mail.gmail.com>
Date:	Wed, 3 Jul 2013 15:09:10 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Li Zefan <lizefan@...wei.com>
Cc:	akpm@...ux-foundation.org, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-next@...r.kernel.org, sfr@...b.auug.org.au,
	linux-mm@...ck.org
Subject: Re: [PATCH next-20130703] net: sock: Add ifdef CONFIG_MEMCG_KMEM for mem_cgroup_sockets_{init,destroy}

On Wed, Jul 3, 2013 at 2:51 PM, Li Zefan <lizefan@...wei.com> wrote:
> On 2013/7/3 20:19, Sedat Dilek wrote:
>> When "CONFIG_MEMCG_KMEM=n" I see this in my build-log:
>>
>>  LD      init/built-in.o
>> mm/built-in.o: In function `mem_cgroup_css_free':
>> memcontrol.c:(.text+0x5caa6): undefined reference to `mem_cgroup_sockets_destroy'
>> make[2]: *** [vmlinux] Error 1
>>
>> Inspired by the ifdef for mem_cgroup_sockets_{init,destroy} here...
>>
>> [ net/core/sock.c ]
>>
>>  #ifdef CONFIG_MEMCG_KMEM
>>  int mem_cgroup_sockets_init()
>>  ...
>>  void mem_cgroup_sockets_destroy()
>>  ...
>>  #endif
>>
>> ...I did the the same for both in "include/net/sock.h".
>>
>> This fixes the issue for me in next-20130703.
>>
>> Signed-off-by: Sedat Dilek <sedat.dilek@...il.com>
>
> Maybe it's better to add memcg_destroy_kmem(), to pair with
> memcg_init_kmem().
>
> This patch can be folded into "memcg: use css_get/put when charging/uncharging kmem"
>

Hi Li Zefan,

Can you or a guru from netdev explain me why there exists
mem_cgroup_sockets_init() and mem_cgroup_sockets_destroy() in

1. net/core/sock.c <--- AFAICS this includes below sock.h, too.
2. net/core/sock.h <--- mm/memcontrol.c is including this one.

Make me less confused.

And can you explain why your approach is "better" to do the change in
memcontrol.c than in sock.h (see sock.c).

Thanks in advance.

- Sedat -

> =======================
>
> [PATCH] memcg: fix build error if CONFIG_MEMCG_KMEM=n
>
> Fix this build error:
>
> mm/built-in.o: In function `mem_cgroup_css_free':
> memcontrol.c:(.text+0x5caa6): undefined reference to
> 'mem_cgroup_sockets_destroy'
>
> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Li Zefan <lizefan@...wei.com>
> ---
>  mm/memcontrol.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 234f311..59ea6f9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5876,6 +5876,11 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>         return mem_cgroup_sockets_init(memcg, ss);
>  }
>
> +static void memcg_destroy_kmem(struct mem_cgroup *memcg)
> +{
> +       mem_cgroup_sockets_destroy(memcg);
> +}
> +
>  static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
>  {
>         if (!memcg_kmem_is_active(memcg))
> @@ -5915,6 +5920,10 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>         return 0;
>  }
>
> +static void memcg_destroy_kmem(struct mem_cgroup *memcg)
> +{
> +}
> +
>  static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
>  {
>  }
> @@ -6312,8 +6321,7 @@ static void mem_cgroup_css_free(struct cgroup *cont)
>  {
>         struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
>
> -       mem_cgroup_sockets_destroy(memcg);
> -
> +       memcg_destroy_kmem(memcg);
>         __mem_cgroup_free(memcg);
>  }
>
> --
> 1.8.0.2
>
>
>> ---
>> [ v2: git dislikes lines beginning with hash ('#'). ]
>>
>>  include/net/sock.h | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/sock.h b/include/net/sock.h
>> index ea6206c..ad4bf7f 100644
>> --- a/include/net/sock.h
>> +++ b/include/net/sock.h
>> @@ -71,6 +71,7 @@
>>  struct cgroup;
>>  struct cgroup_subsys;
>>  #ifdef CONFIG_NET
>> +#ifdef CONFIG_MEMCG_KMEM
>
> #if defined(CONFIG_NET) && defined(CONFIG_MEMCG_KMEM)
>
>>  int mem_cgroup_sockets_init(struct mem_cgroup *memcg, struct cgroup_subsys *ss);
>>  void mem_cgroup_sockets_destroy(struct mem_cgroup *memcg);
>>  #else
>> @@ -83,7 +84,8 @@ static inline
>>  void mem_cgroup_sockets_destroy(struct mem_cgroup *memcg)
>>  {
>>  }
>> -#endif
>> +#endif /* CONFIG_NET */
>> +#endif /* CONFIG_MEMCG_KMEM */
>>  /*
>>   * This structure really needs to be cleaned up.
>>   * Most of it is for TCP, and not used by any of
>>
>
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