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8.2. Configuring huge pages on the Compute node

Configure the Compute node to enable instances to request huge pages.

Procedure

  1. Configure the amount of huge page memory to reserve on each NUMA node for processes that are not instances: 

    parameter_defaults:
  NovaReservedHugePages: ["node:0,size:2048,count:64","node:1,size:1GB,count:1"]

    Where:

    Attribute

    Description

    size

    The size of the allocated huge page. Valid values: * 2048 (for 2MB) * 1GB

    count

    The number of huge pages used by OVS per NUMA node. For example, for 4096 of socket memory used by Open vSwitch, set this to 2.

  2. (Optional) To allow instances to allocate 1GB huge pages, configure the CPU feature flags, cpu_model_extra_flags, to include "pdpe1gb": 

    parameter_defaults:
   ComputeExtraConfig:
     nova::compute::libvirt::libvirt_cpu_mode: 'custom'
     nova::compute::libvirt::libvirt_cpu_model: 'Haswell-noTSX'
     nova::compute::libvirt::libvirt_cpu_model_extra_flags: 'vmx, pdpe1gb'
    注記
    • CPU feature flags do not need to be configured to allow instances to only request 2 MB huge pages.
    • You can only allocate 1G huge pages to an instance if the host supports 1G huge page allocation.
    • You only need to set cpu_model_extra_flags to pdpe1gb when cpu_mode is set to host-model or custom.
    • If the host supports pdpe1gb, and host-passthrough is used as the cpu_mode, then you do not need to set pdpe1gb as a cpu_model_extra_flags. The pdpe1gb flag is only included in Opteron_G4 and Opteron_G5 CPU models, it is not included in any of the Intel CPU models supported by QEMU.
    • To mitigate for CPU hardware issues, such as Microarchitectural Data Sampling (MDS), you might need to configure other CPU flags. For more information, see RHOS Mitigation for MDS ("Microarchitectural Data Sampling") Security Flaws.

  3. To avoid loss of performance after applying Meltdown protection, configure the CPU feature flags, cpu_model_extra_flags, to include "+pcid": 

    parameter_defaults:
   ComputeExtraConfig:
     nova::compute::libvirt::libvirt_cpu_mode: 'custom'
     nova::compute::libvirt::libvirt_cpu_model: 'Haswell-noTSX'
     nova::compute::libvirt::libvirt_cpu_model_extra_flags: 'vmx, pdpe1gb, +pcid'
    ヒント
  4. Add NUMATopologyFilter to the NovaSchedulerDefaultFilters parameter in each Compute environment file, if not already present.

  5. Apply this huge page configuration by adding the environment file(s) to your deployment command and deploying the overcloud: 

    (undercloud) $ openstack overcloud deploy --templates \
  -e [your environment files]
  -e /home/stack/templates/<compute_environment_file>.yaml

8.2.1. Allocating huge pages to instances

Create a flavor with the hw:mem_page_size extra specification key to specify that the instance should use huge pages.

Prerequisites

Procedure

  1. Create a flavor for instances that require huge pages: 

    $ openstack flavor create --ram <size-mb> --disk <size-gb> --vcpus <no_reserved_vcpus> huge_pages

  2. Set the flavor for huge pages: 

    $ openstack flavor set huge_pages --property hw:mem_page_size=1GB

    Valid values for hw:mem_page_size:

    • large - Selects the largest page size supported on the host, which may be 2 MB or 1 GB on x86_64 systems.
    • small - (Default) Selects the smallest page size supported on the host. On x86_64 systems this is 4 kB (normal pages).
    • any - Selects the largest available huge page size, as determined by the libvirt driver.
    • <pagesize>: (string) Set an explicit page size if the workload has specific requirements. Use an integer value for the page size in KB, or any standard suffix. For example: 4KB, 2MB, 2048, 1GB.

  3. Create an instance using the new flavor: 

    $ openstack server create --flavor huge_pages --image <image> huge_pages_instance

Validation

The scheduler identifies a host with enough free huge pages of the required size to back the memory of the instance. If the scheduler is unable to find a host and NUMA node with enough pages, then the request will fail with a NoValidHost error.