linux-kernel - Re: [RFC][PATCH 6/7] Account for the number of tasks within container

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Date:	Wed, 07 Mar 2007 10:13:05 +0300
From:	Pavel Emelianov <xemul@...ru>
To:	Paul Menage <menage@...gle.com>
CC:	Andrew Morton <akpm@...l.org>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>, devel@...nvz.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	containers@...ts.osdl.org, Kirill Korotaev <dev@...ru>
Subject: Re: [RFC][PATCH 6/7] Account for the number of tasks within container

Paul Menage wrote:
> Hi Pavel,
> 
> On 3/6/07, Pavel Emelianov <xemul@...ru> wrote:
>> diff -upr linux-2.6.20.orig/include/linux/sched.h
>> linux-2.6.20-0/include/linux/sched.h
>> --- linux-2.6.20.orig/include/linux/sched.h     2007-03-06
>> 13:33:28.000000000 +0300
>> +++ linux-2.6.20-0/include/linux/sched.h        2007-03-06
>> 13:33:28.000000000 +0300
>> @@ -1052,6 +1055,9 @@ struct task_struct {
>>  #ifdef CONFIG_FAULT_INJECTION
>>         int make_it_fail;
>>  #endif
>> +#ifdef CONFIG_PROCESS_CONTAINER
>> +       struct numproc_container *numproc_cnt;
>> +#endif
>>  };
> 
> Why do you need a pointer added to task_struct? One of the main points
> of the generic containers is to avoid every different subsystem and
> resource controller having to add new pointers there.
> 
>> +
>> +       rcu_read_lock();
>> +       np = numproc_from_cont(task_container(current, &numproc_subsys));
>> +       css_get_current(&np->css);
> 
> There's no need to hold a reference here - by definition, the task's
> container can't go away while the task is in it.
> 
> Also, shouldn't you have an attach() method to move the count from one
> container to another when a task moves?

The idea is:

Task may be "the entity that allocates the resources" and "the
entity that is a resource allocated".

When task is the first entity it may move across containers
(that is implemented in your patches). When task is a resource
it shouldn't move across containers like files or pages do.

More generally - allocated resources hold reference to original
container till they die. No resource migration is performed.

Did I express my idea cleanly?

> Paul
> 

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