[mm v2 0/3] Support memory cgroup hotplug

[Balbir Singh]

On 23/11/16 18:25, Michal Hocko wrote:
> On Wed 23-11-16 15:36:51, Balbir Singh wrote:
>> In the absence of hotplug we use extra memory proportional to
>> (possible_nodes - online_nodes) * number_of_cgroups. PPC64 has a patch
>> to disable large consumption with large number of cgroups. This patch
>> adds hotplug support to memory cgroups and reverts the commit that
>> limited possible nodes to online nodes.
> 
> Balbir,
> I have asked this in the previous version but there still seems to be a
> lack of information of _why_ do we want this, _how_ much do we save on
> the memory overhead on most systems and _why_ the additional complexity
> is really worth it. Please make sure to add all this in the cover
> letter.
> 

The data is in the patch referred to in patch 3. The order of waste was
200MB for 400 cgroup directories enough for us to restrict possible_map
to online_map. These patches allow us to have a larger possible map and
allow onlining nodes not in the online_map, which is currently a restriction
on ppc64.

A typical system that I use has about 100-150 directories, depending on the
number of users/docker instances/configuration/virtual machines. These numbers
will only grow as we pack more of these instances on them.

>From a complexity view point, the patches are quite straight forward.

> I still didn't get to look into those patches because I am swamped with
> other things but to be honest I do not really see a strong justification
> to make it high priority for me.
> 

I am OK if you need more time to review them, but I've been pushing them
to fix the cases I've mentioned above.

Balbir Singh.