Why does allocator keep track of the revocable resources separately from regular resources

[Qian AZ Zhang]

Hi,

When I try Mesos oversubscription feature, I found the revocable resources
returned by resource estimator are actually separately kept track by
allocator from regular resources, e.g., I started my slave with this
command:
    ./bin/mesos-slave.sh --master=192.168.122.171:5050
--resource_estimator="org_apache_mesos_FixedResourceEstimator"
--modules=/home/stack/mesos/build/slave_modules

The content of /home/stack/mesos/build/slave_modules is:
    {
      "libraries": {
        "file":
"/home/stack/mesos/build/src/.libs/libfixed_resource_estimator.so",
        "modules": {
        "name": "org_apache_mesos_FixedResourceEstimator",
          "parameters": {
          "key": "resources",
          "value": "cpus:2;mem:500"
          }
        }
      }
    }

Then I see the following message in master's output:
    I0815 23:16:34.065404 23218 hierarchical.hpp:600] Slave
20150815-231543-2876942528-5050-23204-S0 (mesos) updated with
oversubscribed resources cpus(*){REV}:2; mem(*){REV}:500 (total: cpus(*):4;
mem(*):2929; disk(*):36813; ports(*):[31000-32000]; cpus(*){REV}:2; mem
(*){REV}:500, allocated: )

So as you can see, the slave's total resources are: cpus(*):4; mem(*):2929;
disk(*):36813; ports(*):[31000-32000]; cpus(*){REV}:2; mem(*){REV}:500, the
revocable resources (cpus(*){REV}:2; mem(*){REV}:500) are kept separately
from the regular resources (cpus(*):4; mem(*):2929; disk(*):36813; ports
(*):[31000-32000];) which are auto detected when slave started up. That
means frameworks can use more than the auto detected resources which I
think should be slave's total resources. This seems a bit strange to me, I
think allocator needs to mark part of the auto detected resources as
revocable based on what resource estimator returns.


Regards,
Qian Zhang