linux-kernel - Re: [PATCH 7/7] cgroups: Add a max number of tasks subsystem

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Message-ID: <4E2E178B.3000500@cn.fujitsu.com>
Date:	Tue, 26 Jul 2011 09:25:31 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>
Subject: Re: [PATCH 7/7] cgroups: Add a max number of tasks subsystem

Paul Menage wrote:
> On Mon, Jul 11, 2011 at 7:15 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
>>  /* */
>> +
>> +#ifdef CONFIG_CGROUP_MAX_TASKS
>> +SUBSYS(max_tasks)
>> +#endif
> 
> I think I'd be inclined to make the naming slightly (IMO) cleaner:
> call the subsystem 'tasks' and the files 'limit' and 'count' (or maybe
> 'usage' to be more in line with memcg).
>>
>> +config CGROUP_MAX_TASKS
>> +        bool "Control max number of tasks in a cgroup"
>> +       depends on RESOURCE_COUNTERS
>> +       help
>> +         This option let the user to set up an upper bound allowed number
>> +         of tasks.
>> +
> 
> Needs to depend on CGROUPS too?
> 

it's done implicitly, because it's inside "menuconfig CGROUPS".

>> +
>> +
>> +struct task_counter {
>> +       struct res_counter              res;
>> +       struct cgroup_subsys_state      css;
>> +};
> 
> All other CSS structures put the "css" field as the first thing in the
> structure. Not sure that anything relies on that, but consistency

no as far as I know, and that's a bad thing.

> can't hurt and it probably makes the code fractionally smaller since
> the translation between CSS and task_counter becomes a no-op.
> 
>> +static void task_counter_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
>> +                             struct cgroup *old_cgrp, struct task_struct *task)
>> +{
>> +       struct task_counter *cnt = cgroup_task_counter(old_cgrp);
>> +
>> +       if (cnt != &root_counter)
>> +               res_counter_uncharge_until(&cnt->res, &root_counter.res, 1);
>> +}
> 
> Do we even need the root_counter to be exposed in any way? Why not
> make children of the root cgroup just have a NULL parent res_counter?
> 
> You'll still need a task_counter object so that the cgroups framework
> has a CSS object for cgroups housekeeping, but I don't think it needs
> to actually be used for anything.
> 
> Paul
> 
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