linux-kernel - Re: counting file descriptors with a cgroup controller

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Message-ID: <20170307194134.GE31179@htj.duckdns.org>
Date:   Tue, 7 Mar 2017 14:41:34 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Krzysztof Opasiak <k.opasiak@...sung.com>
Cc:     lizefan@...wei.com, hannes@...xchg.org,
        Łukasz Stelmach <l.stelmach@...sung.com>,
        linux-kernel@...r.kernel.org,
        Karol Lewandowski <k.lewandowsk@...sung.com>,
        cgroups@...r.kernel.org
Subject: Re: counting file descriptors with a cgroup controller

Hello, Krzysztof.

On Tue, Mar 07, 2017 at 12:19:52PM +0100, Krzysztof Opasiak wrote:
> So maybe let me clarify our use case so we can have some more discussion
> about this. We are dealing with task of monitoring system services on an IoT
> system. So this system needs to run as long as possible without reboot just
> like server. In server world almost whole system state is being monitored by
> services like nagios. They measure each parameter (like cpu, memory etc)
> with some interval. Unfortunately we cannot use this it in an embedded
> system due to power consumption.

So, we don't add controllers for specific use case scenarios.  The
target actually has to be a fundamental resource which can't be
isolated in a different way.

The use case you're describing is more about working around
shortcomings in userspace by implemneting a major kernel feature, when
the said shortcomings can easily be controlled and mitigated from
userspace - e.g. if running out of fds can't be handled reliably from
the target application for some reason and the application may lock up
from the condition, protect the base resources so that a monitoring
process can always reliably run and let that take a corrective action
when such condition is detected.

This doesn't really seem to qualify as a dedicated kernel
functionality.

Thanks.

-- 
tejun