max_unit is intended, as @edleafe states, to limit requested amount of resources to a sane amount. It is there to provide protection against consuming an amount of resources that would represent an unrealistic request when the allocation_ratio > 1.0.
For example, consider the default CPU allocation ratio is 16.0. Now consider a host has 32 physical CPU processors, and 2 of those are reserved for the host via the reserved_host_cpus CONF option. The max_unit would be 32, because that is the theoretical "sane" limit of vCPUs that a single instance can consume on the host. Remember that the host doesn't have 2 *physical* CPUs reserved for itself. It has 2 VCPU reserved for itself. I'm going to close this as Won't Fix because this is the same behaviour that has existed in Nova since the very beginning (these things were constructed and passed as the "limits" parameter to the resource claim). Bence, I believe that your use case is more properly addressed with the cpu_dedicated_set and cpu_shared_set work that is currently underway and described partly in this blueprint: https://review.openstack.org/#/c/555081/ In the case of dedicated CPUs, the allocation ratio would be 1.0 and the (total - reserved) value would indeed be the limiting factor in calculating whether an instance would be able to consume that amount of resources. ** Changed in: nova Status: Triaged => Won't Fix -- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1749404 Title: nova-compute resource tracker ignores 'reserved' while reporting 'max_unit' Status in OpenStack Compute (nova): Won't Fix Bug description: The following inventory was reported after a fresh devstack build: curl --silent \ --header "Accept: application/json" \ --header "Content-Type: application/json" \ --header "OpenStack-API-Version: placement latest" \ --header "X-Auth-Token: ${TOKEN:?}" \ -X GET http://127.0.0.1/placement/resource_providers/8d4d7926-df76-42e5-b5da-67893468f5cb/inventories | json_pp { "resource_provider_generation" : 1, "inventories" : { "DISK_GB" : { "max_unit" : 19, "min_unit" : 1, "allocation_ratio" : 1, "step_size" : 1, "reserved" : 0, "total" : 19 }, "MEMORY_MB" : { "allocation_ratio" : 1.5, "max_unit" : 5967, "min_unit" : 1, "reserved" : 512, "step_size" : 1, "total" : 5967 }, "VCPU" : { "allocation_ratio" : 16, "min_unit" : 1, "max_unit" : 2, "reserved" : 0, "step_size" : 1, "total" : 2 } } } IMO the correct max_unit value of the MEMORY_MB resource would be (total - reserved). But today it equals the total value. nova commit: 9e9b3e1 devstack commit: fbdefac devstack config: ENABLED_SERVICES+=,placement-api,placement-client To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1749404/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : [email protected] Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp
