[LTP] [RFC PATCH 4/4] memcg_stress_test.sh: allocate less than CommitLimit bytes

[Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>]

On 05/19/2016 04:38 PM, Cyril Hrubis wrote:
> Hi!
>>> I guess that when we decide to create the pressure inside of the memory
>>> cgroup, instead of stressing the whole system, we may as well choose
>>> small enough amount of memory, something as (RAM - 250Mb)/10 and be done
>>> with it.
>>
>> Yes, this should work as well.
>>
>> I don't know how we could stress the whole system without the risk of
>> hitting an OOM. One idea which comes to my mind is about using a
>> top-level control group with a significant amount of memory assigned to
>> it (like mem_free / 2).
>>
>> Could you, please, have a look at the attachment? I was playing with
>> this patch today and was able to stress my system without OOM.
>>
>> However, this scheme may result in a very intensive swapping if mem_free
>> is large (given that there is enough swap).
>
> Then we should place upper limit on the amount of used swap as well.
>
> Something as MIN(MemFree/2, SwapFree, 1GB) to be used for the limit and
> abort the test if this number is to small?

Now, after weekends are gone, I believe that there is no need in an 
extra control group, if we let the tests allocate MemTotal bytes of 
memory. There will always be swapping, and its intensity will not depend 
on the amount of swap space configured, and it will not be "too much" 
unless there are some mm-using processes running on the system.

I believe the attached patch introduces the minimal set of changes to 
the original test case idea (as we understand it), but lets the test 
case runs in different environments.

What do you think about it? Did I miss something?

Thanks.


>
> Apart from that the root memory cgroup should be better named something
> as ltp_stres_root so that it's clear where it came from...
>
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