Re: how to make memory.memsw.failcnt is nonzero

[Peng Haitao <penght@cn.fujitsu.com>]

Michal Hocko said the following on 2012-1-6 18:12:
>> If there is something wrong, I think the bug will be in mem_cgroup_do_charge()
>> of mm/memcontrol.c
>>
>> 2210         ret = res_counter_charge(&memcg->res, csize, &fail_res);
>> 2211 
>> 2212         if (likely(!ret)) {
...
>> 2221                 flags |= MEM_CGROUP_RECLAIM_NOSWAP;
>> 2222         } else
>> 2223                 mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
>>
>> When hit memory.limit_in_bytes, res_counter_charge() will return -ENOMEM,
>> this will execute line 2222: } else.
>> But I think when hit memory.limit_in_bytes, the function should determine further
>> to memory.memsw.limit_in_bytes.
>> This think is OK?
> 
> I don't think so. We have an invariant (hard limit is "stronger" than
> memsw limit) memory.limit_in_bytes <= memory.memsw.limit_in_bytes so
> when we hit the hard limit we do not have to consider memsw because
> resource counter:
>  a) we already have to do reclaim for hard limit
>  b) we check whether we might swap out later on in
>  mem_cgroup_hierarchical_reclaim (root_memcg->memsw_is_minimum) so we
>  will not end up swapping just to make hard limit ok and go over memsw
>  limit.
> 
> Please also note that we will retry charging after reclaim if there is a
> chance to meet the limit.
> Makes sense?

Yeah.

But I want to test memory.memsw.failcnt is nonzero, how steps?
Thanks.

-- 
Best Regards,
Peng