Re: [RESEND][v1 0/3] Support memory cgroup hotplug

[Balbir Singh <bsingharora@gmail.com>]

On 22/11/16 01:03, Michal Hocko wrote:
> On Wed 16-11-16 10:44:58, 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.
> 
> I didn't get to read patches yet (I am currently swamped by emails after
> longer vacation so bear with me) but this doesn't tell us _why_ we want
> this and how much we can actaully save. 

The motivation was 3af229f2071f
(powerpc/numa: Reset node_possible_map to only node_online_map)

In general being dynamic is more
> complex and most systems tend to have possible_nodes close to
> online_nodes in my experience (well at least on most reasonable
> architectures). I would also appreciate some highlevel description of
> the implications. E.g. how to we synchronize with the hotplug operations
> when iterating node specific data structures.

I agree dynamic is more complex, but I think we'll begin to see a lot
of more of it. The rules are not hard IMHO. From an implication perspective
it means that we need to get/put_online_mem_nodes in certain paths - specifically
mem_cgroup_alloc/free and mem_cgroup_init from what I can see so far

Thanks for the review!

Balbir Singh

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