[Devel] Re: [PATCH 08/10] memcg: Add CONFIG_CGROUP_MEM_RES_CTLR_KMEM_ACCT_ROOT.

[Suleiman Souhlal]

On Wed, Feb 29, 2012 at 9:09 AM, Glauber Costa <glommer at parallels.com> wrote:
> On 02/28/2012 08:36 PM, Suleiman Souhlal wrote:
>>
>> On Tue, Feb 28, 2012 at 5:34 AM, Glauber Costa<glommer at parallels.com>
>>  wrote:
>>>
>>> On 02/27/2012 07:58 PM, Suleiman Souhlal wrote:
>>>>
>>>>
>>>> This config option dictates whether or not kernel memory in the
>>>> root cgroup should be accounted.
>>>>
>>>> This may be useful in an environment where everything is supposed to be
>>>> in a cgroup and accounted for. Large amounts of kernel memory in the
>>>> root cgroup would indicate problems with memory isolation or accounting.
>>>
>>>
>>>
>>> I don't like accounting this stuff to the root memory cgroup. This causes
>>> overhead for everybody, including people who couldn't care less about
>>> memcg.
>>>
>>> If it were up to me, we would simply not account it, and end of story.
>>>
>>> However, if this is terribly important for you, I think you need to at
>>> least make it possible to enable it at runtime, and default it to
>>> disabled.
>>
>>
>> Yes, that is why I made it a config option. If the config option is
>> disabled, that memory does not get accounted at all.
>
>
> Doesn't work. In reality, most of the distributions enable those stuff if
> there is the possibility that someone will end up using. So everybody gets
> to pay the penalty.
>
>
>> Making it configurable at runtime is not ideal, because we would
>> prefer slab memory that was allocated before cgroups are created to
>> still be counted toward root.
>>
>
> Again: Why is that you really need it ? Accounting slab to the root cgroup
> feels quite weird to me

Because, for us, having large amounts of unaccounted memory is a
"bug", and we would like to know when it happens.
Also, we want to know how much memory is actually available in the
machine for jobs (sum of(accounted memory in containers) - unaccounted
kernel memory).

That said, I will drop this patch from the series for now.

-- Suleiman