linux-kernel - Re: [PATCH] cgroup

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Message-ID: <564A0C0E.6090004@gmail.com>
Date:	Mon, 16 Nov 2015 12:02:06 -0500
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Aleksa Sarai <cyphar@...har.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

On 2015-11-15 08:36, Aleksa Sarai wrote:
>>> 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.
OK, what specific resources back each of the things that I mentioned? 
Other than setting up a new process (which in retrospect I realize 
should probably just be accounted as processor time for the parent), I 
can't really see much that most of these are backed by, other than 
processor time (and until someone demonstrates otherwise, I stand by my 
statement that they are non-trivial to account properly as processor time).


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