Re: [PATCH] new cgroup controller "fork"

[Li Zefan <lizf@cn.fujitsu.com>]

于 2011年11月04日 05:54, Glauber Costa 写道:
> On 11/03/2011 06:13 PM, Brian K. White wrote:
>> On 11/3/2011 3:25 PM, Glauber Costa wrote:
>>> On 11/03/2011 05:20 PM, Max Kellermann wrote:
>>>> On 2011/11/03 20:03, Alan Cox<alan@lxorguk.ukuu.org.uk> wrote:
>>>>> Sure - I'm just not seeing that a whole separate cgroup for it is
>>>>> appropriate or a good plan. Anyone doing real resource management needs
>>>>> the rest of the stuff anyway.
>>>>
>>>> Right. When I saw Frederic's controller today, my first thought was
>>>> that one could move the fork limit code over into that controller. If
>>>> we reach a consensus that this would be a good idea, and would have
>>>> chances to get merged, I could probably take some time to refactor my
>>>> code.
>>>>
>>>> Max
>>> I'd advise you to take a step back and think if this is really needed.
>>> As Alan pointed out, the really expensive resource here is already being
>>> constrained by Frederic's controller.
>>
>> I think this really is a different knob that is nice to have as long as
>> it doesn't cost much. It's a way to set a max lifespan in a way that
>> isn't really addressed by the other controls. (I could absolutely be
>> missing something.)
>>
>> I think Max explained the issue clearly enough.
> 
> He did, indeed.
> 
>> It doesn't matter that the fork itself is supposedly so cheap.
>>
>> It's still nice to have a way to say, you may not fork/die/fork/die/fork
>> in a race.
>>
>> What's so unimaginable about having a process that you know needs a lot
>> of cpu and ram or other resources to do it's job, and you expressly want
>> to allow it to take as much of those resources as it can, but you know
>> it has no need to fork, so if it forks, _that_ is the only indication of
>> a problem, so you may only want to block it based on that.
>>
>> Sure many other processes would legitimately fork/die/fork/die a lot
>> while never exceeding a few total concurrent tasks, and for them you
>> would not want to set any such fork limit. So what?
>>
> As I said previously, he knows his use cases better than anyone else.
> If a use case can be found in which the summation of cpu+task controllers is not enough, and if this is implemented as an option to the task controller, and does not make it:
> 1) confusing,
> 2) more expensive,
> 
> then I don't see why not we shouldn't take it.

Quoted from Lennart's reply in another mail thread:

"Given that shutting down some services might involve forking off a few
things (think: a shell script handling shutdown which forks off a couple
of shell utilities) we'd want something that is between "from now on no
forking at all" and "unlimited forking". This could be done in many
different ways: we'd be happy if we could do time-based rate limiting,
but we'd also be fine with defining a certain budget of additional forks
a cgroup can do (i.e. "from now on you can do 50 more forks, then you'll
get EPERM)."

(http://lkml.org/lkml/2011/10/19/468)

The last sentence suggests he might like this fork controller.