Let's discuss on code with changes after your commits to v2 to have them made visible.
v3 is on the way
Kirill
On 24.04.2018 14:28, Vladimir Davydov wrote:
> On Mon, Apr 23, 2018 at 01:54:50PM +0300, Kirill Tkhai wrote:
>>>> @@ -1200,6 +1206,8 @@ extern int memcg_nr_cache_ids;
>>>> void memcg_get_cache_ids(void);
>>>> void memcg_put_cache_ids(void);
>>>>
>>>> +extern int shrinkers_max_nr;
>>>> +
>>>
>>> memcg_shrinker_id_max?
>>
>> memcg_shrinker_id_max sounds like an includive value, doesn't it?
>> While shrinker->id < shrinker_max_nr.
>>
>> Let's better use memcg_shrinker_nr_max.
>
> or memcg_nr_shrinker_ids (to match memcg_nr_cache_ids), not sure...
>
> Come to think of it, this variable is kinda awkward: it is defined in
> vmscan.c but declared in memcontrol.h; it is used by vmscan.c for max
> shrinker id and by memcontrol.c for shrinker map capacity. Just a raw
> idea: what about splitting it in two: one is private to vmscan.c, used
> as max id, say we call it shrinker_id_max; the other is defined in
> memcontrol.c and is used for shrinker map capacity, say we call it
> memcg_shrinker_map_capacity. What do you think?
>
>>>> +int expand_shrinker_maps(int old_nr, int nr)
>>>> +{
>>>> + int id, size, old_size, node, ret;
>>>> + struct mem_cgroup *memcg;
>>>> +
>>>> + old_size = old_nr / BITS_PER_BYTE;
>>>> + size = nr / BITS_PER_BYTE;
>>>> +
>>>> + down_write(&shrinkers_max_nr_rwsem);
>>>> + for_each_node(node) {
>>>
>>> Iterating over cgroups first, numa nodes second seems like a better idea
>>> to me. I think you should fold for_each_node in memcg_expand_maps.
>>>
>>>> + idr_for_each_entry(&mem_cgroup_idr, memcg, id) {
>>>
>>> Iterating over mem_cgroup_idr looks strange. Why don't you use
>>> for_each_mem_cgroup?
>>
>> We want to allocate shrinkers maps in mem_cgroup_css_alloc(), since
>> mem_cgroup_css_online() mustn't fail (it's a requirement of currently
>> existing design of memcg_cgroup::id).
>>
>> A new memcg is added to parent's list between two of these calls:
>>
>> css_create()
>> ss->css_alloc()
>> list_add_tail_rcu(&css->sibling, &parent_css->children)
>> ss->css_online()
>>
>> for_each_mem_cgroup() does not see allocated, but not linked children.
>
> Why don't we move shrinker map allocation to css_online then?
>
>>
>>>> + if (id == 1)
>>>> + memcg = NULL;
>>>> + ret = memcg_expand_maps(memcg, node, size, old_size);
>>>> + if (ret)
>>>> + goto unlock;
>>>> + }
>>>> +
>>>> + /* root_mem_cgroup is not initialized yet */
>>>> + if (id == 0)
>>>> + ret = memcg_expand_maps(NULL, node, size, old_size);
>>>> + }
>>>> +unlock:
>>>> + up_write(&shrinkers_max_nr_rwsem);
>>>> + return ret;
>>>> +}
