linux-kernel - Re: [PATCH] cgroup

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Message-ID: <CAOviyag=rHcDZj3MBR3dMbkdaOY=h1FB-78QLM3CZQe2WrrgCQ@mail.gmail.com>
Date:	Mon, 16 Nov 2015 00:36:44 +1100
From:	Aleksa Sarai <cyphar@...har.com>
To:	Austin S Hemmelgarn <ahferroin7@...il.com>
Cc:	Parav Pandit <pandit.parav@...il.com>,
	Max Kellermann <mk@...all.com>, Tejun Heo <tj@...nel.org>,
	cgroups@...r.kernel.org, lizefan@...wei.com,
	Johannes Weiner <hannes@...xchg.org>, max@...mpel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup_pids: add fork limit

>> If so, could you share little more insight on how that time measure
>> outside of the cpu's cgroup cycles? Just so that its helpful to wider
>> audience.
>
> Well, there are a number of things that I can think of that the kernel does
> on behalf of processes that can consume processor time that isn't trivial to
> account:
>   * Updating timers on behalf of userspace processes (itimers or similar).
>   * Sending certain kernel generated signals to processes (that is, stuff
> generated by the kernel like SIGFPE, SIGSEGV, and so forth).
>   * Queuing events from dnotify/inotify/fanotify.
>   * TLB misses, page faults, and swapping.
>   * Setting up new processes prior to them actually running.
>   * Scheduling.
> All of these are things that fork-bombs can and (other than TLB misses) do
> exploit to bring a system down, and the cpu cgroup is by no means a magic
> bullet to handle this.

I feel like these are backed by different resources, and we should
work on limiting those *at the source* in the context of a controller
rather than just patching up the symptoms (too many forks causing
issues), because these are symptoms of a larger issue IMO.

-- 
Aleksa Sarai (cyphar)
www.cyphar.com
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