Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

[Pavel Emelyanov <xemul@parallels.com>]

On 11/11/2011 09:02 PM, Tejun Heo wrote:
> Hello,
> 
> On Fri, Nov 11, 2011 at 08:49:50PM +0400, Pavel Emelyanov wrote:
>> 1 cpu 500k forks                                         - 37s
> 
> That's ~14k forks per sec.  Do you still think you need parallel
> forking?
> 
>> 2 cpus on different cores 500k forks on each in parallel - 39s
>> 4 cpus on different cores 500k forks on each in parallel - 41s
>>
>> 8 cpus 500k forks on each in parallel                    - 1m5s
>>
>> So the fork() scaling seems quite good to me.
> 
> Yeah, looks pretty good actually.  Hmmm, this is on a single socket w/
> shared cache where cacheline bouncing is quite cheap, right?  Also,
> how are those forking processes related?  On multiple sockets, it's
> gonna scale worse.  Dunno how much tho.
> 
> At any rate, if you do the rest in paralllel, whether forking is
> parallel or not is immaterial.  Let's just do something least
> intrusive.

Hm, so intrusiveness is your main concern here, I see.

OK, let's assume we go with sysctl setting the last_pid.

One of the major concerns with previous attempts have been - someone creates 
a process with a pid that was in use by some app recently and screws things 
up with pid reuse. My approach solves this, how can sysctl handle it? Allowing 
the last_pid change by the CAP_SYA_ADMIN only is not an option, since people
are looking forward to non-root restore.

> Thanks.
>