Re: [PATCH 4/4] pidns: Use task_active_pid_ns where appropriate

From: Daniel Lezcano <daniel.lezcano@free.fr>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: akpm@linux-foundation.org, ebiederm@xmission.com,
	oleg@redhat.com, containers@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, clg@fr.ibm.com
Subject: Re: [PATCH 4/4] pidns: Use task_active_pid_ns where appropriate
Date: Mon, 31 Jan 2011 15:47:58 +0100	[thread overview]
Message-ID: <4D46CB9E.1090802@free.fr> (raw)
In-Reply-To: <AANLkTikjcou-0b4NejpY66qXeZuzsC-M+oNTyHk=OE-Z@mail.gmail.com>

On 01/31/2011 12:26 PM, Alexey Dobriyan wrote:
> On Mon, Jan 31, 2011 at 12:25 PM, Daniel Lezcano<daniel.lezcano@free.fr>  wrote:
>> The expressions tsk->nsproxy->pid_ns and task_active_pid_ns
>> aka ns_of_pid(task_pid(tsk)) should have the same number of
>> cache line misses with the practical difference that
>> ns_of_pid(task_pid(tsk)) is released later in a processes life.
>>
>> Furthermore by using task_active_pid_ns it becomes trivial
>> to write an unshare implementation for the the pid namespace.
>>
>> So I have used task_active_pid_ns everywhere I can.
> Yet current->nsproxy->pid_ns is way clearer.
> Because live current always has pid_ns.
>
> This task_active_pid_ns() is misnamed(?) because it does matter only
> for dead tasks?

Actually this function is later used, for the unshare, to get the pid_ns 
of a specific task, not the current one.

http://kerneltrap.org/mailarchive/linux-kernel/2010/6/20/4585095

Do you suggest task_pid_ns(struct task_struct *tsk) would be a better name ?

>> -               current->nsproxy->pid_ns->last_pid);
>> +               task_active_pid_ns(current)->last_pid);
> I thought of doing exactly opposite patch :-)
>