Re: [PATCH -V4 04/10] memcg: Add HugeTLB extension

[Aneesh Kumar K.V]

Michal Hocko <mhocko@xxxxxxx> writes:

> On Fri 16-03-12 23:09:24, Aneesh Kumar K.V wrote:
> [...]
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 6728a7a..4b36c5e 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
> [...]
>> @@ -4887,6 +5013,7 @@ err_cleanup:
>>  static struct cgroup_subsys_state * __ref
>>  mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>>  {
>> +	int idx;
>>  	struct mem_cgroup *memcg, *parent;
>>  	long error = -ENOMEM;
>>  	int node;
>> @@ -4929,9 +5056,14 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>>  		 * mem_cgroup(see mem_cgroup_put).
>>  		 */
>>  		mem_cgroup_get(parent);
>> +		for (idx = 0; idx < HUGE_MAX_HSTATE; idx++)
>> +			res_counter_init(&memcg->hugepage[idx],
>> +					 &parent->hugepage[idx]);
>
> Hmm, I do not think we want to make groups deeper in the hierarchy
> unlimited as we cannot reclaim. Shouldn't we copy the limit from the parent?
> Still not ideal but slightly more expected behavior IMO.

But we should be limiting the child group based on parent's limit only
when hierarchy is set right ?

>
> The hierarchy setups are still interesting and the limitations should be
> described in the documentation...
>

It should behave similar to memcg. ie, if hierarchy is set, then we limit
using MIN(parent's limit, child's limit). May be I am missing some of
the details of memcg use_hierarchy config. My goal was to keep it
similar to memcg. Can you explain why do you think the patch would
make it any different ?

-aneesh

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