website/content/en/docs/tasks/manage-hugepages/scheduling-hugepages.md

reviewers, title, content_template

reviewers	title	content_template
derekwaynecarr	Manage HugePages	templates/task

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Kubernetes supports the allocation and consumption of pre-allocated huge pages by applications in a Pod as a GA feature. This page describes how users can consume huge pages and the current limitations.

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1. Kubernetes nodes must pre-allocate huge pages in order for the node to report its huge page capacity. A node can pre-allocate huge pages for multiple sizes.

The nodes will automatically discover and report all huge page resources as schedulable resources.

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API

Huge pages can be consumed via container level resource requirements using the resource name hugepages-<size>, where <size> is the most compact binary notation using integer values supported on a particular node. For example, if a node supports 2048KiB and 1048576KiB page sizes, it will expose a schedulable resources hugepages-2Mi and hugepages-1Gi. Unlike CPU or memory, huge pages do not support overcommit. Note that when requesting hugepage resources, either memory or CPU resources must be requested as well.

A pod may consume multiple huge page sizes in a single pod spec. In this case it must use medium: HugePages-<hugepagesize> notation for all volume mounts.

apiVersion: v1
kind: Pod
metadata:
  name: huge-pages-example
spec:
  containers:
  - name: example
    image: fedora:latest
    command:
    - sleep
    - inf
    volumeMounts:
    - mountPath: /hugepages-2Mi
      name: hugepage-2mi
    - mountPath: /hugepages-1Gi
      name: hugepage-1gi
    resources:
      limits:
        hugepages-2Mi: 100Mi
        hugepages-1Gi: 2Gi
        memory: 100Mi
      requests:
        memory: 100Mi
  volumes:
  - name: hugepage-2mi
    emptyDir:
      medium: HugePages-2Mi
  - name: hugepage-1gi
    emptyDir:
      medium: HugePages-1Gi

A pod may use medium: HugePages only if it requests huge pages of one size.

apiVersion: v1
kind: Pod
metadata:
  name: huge-pages-example
spec:
  containers:
  - name: example
    image: fedora:latest
    command:
    - sleep
    - inf
    volumeMounts:
    - mountPath: /hugepages
      name: hugepage
    resources:
      limits:
        hugepages-2Mi: 100Mi
        memory: 100Mi
      requests:
        memory: 100Mi
  volumes:
  - name: hugepage
    emptyDir:
      medium: HugePages

• Huge page requests must equal the limits. This is the default if limits are specified, but requests are not.
• Huge pages are isolated at a container scope, so each container has own limit on their cgroup sandbox as requested in a container spec.
• EmptyDir volumes backed by huge pages may not consume more huge page memory than the pod request.
• Applications that consume huge pages via shmget() with SHM_HUGETLB must run with a supplemental group that matches proc/sys/vm/hugetlb_shm_group.
• Huge page usage in a namespace is controllable via ResourceQuota similar to other compute resources like cpu or memory using the hugepages-<size> token.
• Support of multiple sizes huge pages is feature gated. It can be enabled with the HugePageStorageMediumSize feature gate on the {{< glossary_tooltip text="kubelet" term_id="kubelet" >}} and {{< glossary_tooltip text="kube-apiserver" term_id="kube-apiserver" >}} (--feature-gates=HugePageStorageMediumSize=true).

Future

• NUMA locality guarantees as a feature of quality of service.
• LimitRange support.

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