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Brief Description
-----------------
Issue:
After deployment, created maximum numbers of VM's and then changed cpu_allocation_ratio and ram_allocation value in nova.conf of both compute nodes to achieve overcommit of CPU and RAM resources but Memory value doesn't reach maximum value according to overcommitted value.


#Physical CPU and RAM on compute0 
[root@Ctrl0 ~]# openstack host show Comp0
+-------+----------------------------------+-----+-----------+---------+
| Host  | Project                          | CPU | Memory MB | Disk GB |
+-------+----------------------------------+-----+-----------+---------+
| Comp0 | (total)                          |  40 |    322094 |   54387 |
+-------+----------------------------------+-----+-----------+---------+

#Physical CPU on compute1 
[root@Ctrl0 ~]# openstack host show Comp1
+-------+----------------------------------+-----+-----------+---------+
| Host  | Project                          | CPU | Memory MB | Disk GB |
+-------+----------------------------------+-----+-----------+---------+
| Comp1 | (total)                          |  40 |    322099 |   54387 |
+-------+----------------------------------+-----+-----------+---------+

#Changed cpu_allocation_ratio and ram_allocation_ratio values in nova.conf of both compute nodes 
[root@Comp0 ~]# grep "cpu_allocation_ratio" /etc/kolla/nova-compute/nova.conf
cpu_allocation_ratio = 8.0
[root@Comp0 ~]# grep "ram_allocation_ratio" /etc/kolla/nova-compute/nova.conf
ram_allocation_ratio = 16.0
[root@Comp0 ~]#


[root@Comp1 ~]# grep "cpu_allocation_ratio" /etc/kolla/nova-compute/nova.conf
cpu_allocation_ratio = 8.0
[root@Comp1 ~]# grep "ram_allocation_ratio" /etc/kolla/nova-compute/nova.conf
ram_allocation_ratio = 16.0
[root@Comp1 ~]#


#Current vCPU and Memory consumption in system
Hostname	Type	VCPUs (used)	VCPUs (total)	RAM (used)	RAM (total)	Local Storage (used)	Local Storage (total)	Instances
Comp0		QEMU	130					40		   360.5GB			314.5GB			4.1TB		    53.1TB						39
Comp1		QEMU	118					40		   340.5GB			314.5GB			3.2TB		    53.1TB						34
                       
VCPU Usage
Used 248 of 80

Memory Usage
Used 701GB of 629.1GB

#After Creating multiple instance, we will be able to reach maximum vCPU
and RAM consumption to,

VCPU Usage
Used 312 of 80

Memory Usage
Used 813GB of 629.1GB

According to arch design mentioned in below link 
https://docs.openstack.org/arch-design/design-compute/design-compute-overcommit.html

Overcommit of resources are not done for ram_allocation_ratio.. After 813GB usage of RAM we are not able to make more instance of 8GB of RAM.
---------------------------------------------------------------------------------------------------------------------------------------------

#Physical Memory of Both nodes 
[root@Comp0 ~]# free -g
              total        used        free      shared  buff/cache   available
Mem:            314         306           6           0           2           0
Swap:            31          31           0

[root@Comp1 ~]# free -g
              total        used        free      shared  buff/cache   available
Mem:            314         282          16           0          15          19
Swap:            31          23           8
[root@Comp1 ~]#
----------------------------------------------------------------------------------------------------------------------------------------------

#Schedular filters in the system
scheduler_weight_classes = nova.scheduler.weights.all_weighers

[filter_scheduler]
available_filters = nova.scheduler.filters.all_filters
enabled_filters = AvailabilityZoneFilter,ComputeFilter,ComputeCapabilitiesFilter,ImagePropertiesFilter
----------------------------------------------------------------------------------------------------------------------------------------------

Kindly please share your valuable inputs regarding this overcommit ratio settings in the system.
Also please correct us to achieve overcommit of vCPU and RAM resources.

** Affects: nova
     Importance: Undecided
         Status: New

-- 
Resource are not overcommitted when  cpu_allocation_ratio and ram_allocation _ratio value is set in nova.conf
https://bugs.launchpad.net/bugs/1955618
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