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

[Michal Hocko]

On Wed 18-05-16 16:39:18, Cyril Hrubis wrote:
[...]
> Michal is there a way to figure out how much memory should be allocated
> and faulted on a system in order to cause some amount of pages to be
> swapped back and forth?

that depends on how the memory is used. If it is largerly anonymous then
you will get swap out when you hit watermarks.
 
> What this testcase does it to create a process(es) that allocate memory
> and read/write it concurently to stress the system a bit but the
> estimate on how much memory it should use is wrong and it causes OOM
> when the amount of swap is much less than amount of RAM.

Are we talking about memcg or the global here?
 
> The original testcase[1] drops caches then runs child(s) to allocate
> (in sum) MemFree + SwapFree/2 memory. Each child runs in its own memory
> cgroup but the amount of memory was choosen so that the whole system
> would be under memory pressure. Does such test even make sense to you?

Well, it depends. It makes sense to see how the global memory pressure
gets distributed into two memcgs which are the source of that pressure
but I am not really sure how you want to evaluate good vs. bad case as
the load will be quite timing sensitive. So the main question would be,
what do you expect the test will tell you?
 
> [1]:
> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
> 
> -- 
> Cyril Hrubis
> chrubis@suse.cz

-- 
Michal Hocko
SUSE Labs