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. 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.

Thanks!

-- 
Michal Hocko
SUSE Labs