linux-kernel - Re: Cgroups "pids" controller does not update "pids.current" count immediately

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Message-ID: <1d635d1d-6152-ecfc-d235-147ff1fe7c95@icdsoft.com>
Date:   Fri, 15 Jun 2018 19:07:27 +0300
From:   Ivan Zahariev <famzah@...soft.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Cgroups "pids" controller does not update "pids.current" count
 immediately

Hi,

Thank you for the quick and insightful reply. I have one suggestion below:

On 15.6.2018 г. 18:41 ч., Tejun Heo wrote:
> On Fri, Jun 15, 2018 at 05:26:04PM +0300, Ivan Zahariev wrote:
>> The standard RLIMIT_NPROC does not suffer from such accounting
>> discrepancies at any time.
> They seem equivalent but serve a bit different purposes.  RLIMIT_NPROC
> is primarily about limiting what the user can do and doesn't guarantee
> that that actually matches resource (pid here) consumption.
>
>> Is it really technically not possible to make "pids.current" do
>> accounting properly like RLIMIT_NPROC does? We were hoping to
>> replace RLIMIT_NPROC with the "pids" controller.
> It is of course possible but at a cost.  The cost (getting rid of lazy
> release optimizations) is just not justifiable for most cases.

I understand all concerns and design decisions. However, having 
RLIMIT_NPROC support combined with "cgroups" hierarchy would be very handy.

Does it make sense that you introduce "nproc.current" and "nproc.max" 
metrics which work in the same atomic, real-time way like RLIMIT_NPROC? 
Or make this in a new "nproc" controller?

--
Ivan
--