On 23/11/16 19:07, Michal Hocko wrote: > On Wed 23-11-16 18:50:42, Balbir Singh wrote: >> >> >> 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. > > How common is to have possible_map >> online_map? If this is ppc64 then > what is the downside of keeping the current restriction instead? > On my system CONFIG_NODE_SHIFT is 8, 256 nodes and possible_nodes are 2 The downside is the ability to hotplug and online an offline node. Please see http://www.spinics.net/lists/linux-mm/msg116724.html >> 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. > > Well, I would like to hear more about that. {get,put}_online_memory > at random places doesn't sound all that straightforward to me. > I thought those places were not random :) I tried to think them out as discussed with Vladimir. I don't claim the code is bug free, we can fix any bugs as we test this more. Balbir Singh. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>