[v4,2/2] sock: Move the socket inuse to namespace.

This patch add a member in struct netns_core. And this is
a counter for socket_inuse in the _net_ namespace. The patch
will add/sub counter in the sk_alloc or sk_free. Because socket and
sock is in pair. It's a easy way to maintain the code and help
developer to review. More important, it avoids holding the _net_
namespace again.

Signed-off-by: Martin Zhang <zhangjunweimartin@didichuxing.com>
Signed-off-by: Tonghao Zhang <zhangtonghao@didichuxing.com>
---
v3 --> v4:
1. add noop function for !CONF_PROC_FS case.
2. change the __this_cpu_add to this_cpu_add. This is reported by lkp.
reported at: http://patchwork.ozlabs.org/patch/837424/
---
 include/net/netns/core.h |  1 +
 include/net/sock.h       |  1 +
 net/core/sock.c          | 40 +++++++++++++++++++++++++++++++++++++++-
 net/socket.c             | 13 ++-----------
 4 files changed, 43 insertions(+), 12 deletions(-)

From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Date: Wed, 22 Nov 2017 17:51:25 -0800

> This patch add a member in struct netns_core. And this is
> a counter for socket_inuse in the _net_ namespace. The patch
> will add/sub counter in the sk_alloc or sk_free. Because socket and
> sock is in pair. It's a easy way to maintain the code and help
> developer to review. More important, it avoids holding the _net_
> namespace again.
> 
> Signed-off-by: Martin Zhang <zhangjunweimartin@didichuxing.com>
> Signed-off-by: Tonghao Zhang <zhangtonghao@didichuxing.com>

First, it is extremely unclear why this is better.  You do not explain
the reason at all.

Second:

> @@ -2646,17 +2646,8 @@ static int __init sock_init(void)
>  #ifdef CONFIG_PROC_FS
>  void socket_seq_show(struct seq_file *seq)
>  {
> -	int cpu;
> -	int counter = 0;
> -
> -	for_each_possible_cpu(cpu)
> -	    counter += per_cpu(sockets_in_use, cpu);
> -
> -	/* It can be negative, by the way. 8) */
> -	if (counter < 0)
> -		counter = 0;
> -
> -	seq_printf(seq, "sockets: used %d\n", counter);

You've deleted the only use of "sockets_in_use" but you have not
removed that per-cpu variable and it's maintainence.

But do not even bother fixing this if you cannot explain properly
why these changes are an improvement.  I do not understant it,
and until I do I cannot consider these changes seriously.

Thank you.

On Sat, Nov 25, 2017 at 10:53 PM, David Miller <davem@davemloft.net> wrote:
> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> Date: Wed, 22 Nov 2017 17:51:25 -0800
>
>> This patch add a member in struct netns_core. And this is
>> a counter for socket_inuse in the _net_ namespace. The patch
>> will add/sub counter in the sk_alloc or sk_free. Because socket and
>> sock is in pair. It's a easy way to maintain the code and help
>> developer to review. More important, it avoids holding the _net_
>> namespace again.
>>
>> Signed-off-by: Martin Zhang <zhangjunweimartin@didichuxing.com>
>> Signed-off-by: Tonghao Zhang <zhangtonghao@didichuxing.com>
>
> First, it is extremely unclear why this is better.  You do not explain
> the reason at all.
Sorry, I am so later to reply. I send  the v5 and the comment may
explain the reason.

> Second:
>
>> @@ -2646,17 +2646,8 @@ static int __init sock_init(void)
>>  #ifdef CONFIG_PROC_FS
>>  void socket_seq_show(struct seq_file *seq)
>>  {
>> -     int cpu;
>> -     int counter = 0;
>> -
>> -     for_each_possible_cpu(cpu)
>> -         counter += per_cpu(sockets_in_use, cpu);
>> -
>> -     /* It can be negative, by the way. 8) */
>> -     if (counter < 0)
>> -             counter = 0;
>> -
>> -     seq_printf(seq, "sockets: used %d\n", counter);
>
> You've deleted the only use of "sockets_in_use" but you have not
> removed that per-cpu variable and it's maintainence.
So sorry :(

> But do not even bother fixing this if you cannot explain properly
> why these changes are an improvement.  I do not understant it,
> and until I do I cannot consider these changes seriously.
Yes, I should check the patch carefully and add more detail. I may do it better.
The v5 patch may be useful. Thanks so much.

> Thank you.