// github/kubernetes/pkg/apis/core/v1/helper/qos/qos.go
func GetPodQOS(pod *v1.Pod) v1.PodQOSClass {
  requests := v1.ResourceList{}
  limits := v1.ResourceList{}
  zeroQuantity := resource.MustParse("0")
  isGuaranteed := true
  allContainers := []v1.Container{}
  allContainers = append(allContainers, pod.Spec.Containers...)
  // InitContainers 容器也会被加入 QoS 的计算中
  allContainers = append(allContainers, pod.Spec.InitContainers...)
  for _, container := range allContainers {
    // 遍历 requests 中的 CPU 和 memory 值
    for name, quantity := range container.Resources.Requests {
      if !isSupportedQoSComputeResource(name) {
        continue
      }
      if quantity.Cmp(zeroQuantity) == 1 {
        delta := quantity.DeepCopy()
        if _, exists := requests[name]; !exists {
          requests[name] = delta
        } else {
          delta.Add(requests[name])
          requests[name] = delta
        }
      }
    }
    // 遍历 limits 中的 CPU 和 memory 值
    qosLimitsFound := sets.NewString()
    for name, quantity := range container.Resources.Limits {
      if !isSupportedQoSComputeResource(name) {
        continue
      }
      if quantity.Cmp(zeroQuantity) == 1 {
        qosLimitsFound.Insert(string(name))
        delta := quantity.DeepCopy()
        if _, exists := limits[name]; !exists {
          limits[name] = delta
        } else {
          delta.Add(limits[name])
          limits[name] = delta
        }
      }
    }
    // 判断是否同时设置了 limits 和 requests，如果没有则不是 Guaranteed
    if !qosLimitsFound.HasAll(string(v1.ResourceMemory), string(v1.ResourceCPU)) {
      isGuaranteed = false
    }
  }
  // 如果 requests 和 limits 都没有设置，则为 BestEffort
  if len(requests) == 0 && len(limits) == 0 {
    return v1.PodQOSBestEffort
  }
  // 检查所有资源的 requests 和 limits 是否都相等
  if isGuaranteed {
    for name, req := range requests {
      if lim, exists := limits[name]; !exists || lim.Cmp(req) != 0 {
        isGuaranteed = false
        break
      }
    }
  }
  // 都设置了 requests 和 limits，则为 Guaranteed
  if isGuaranteed &&
    len(requests) == len(limits) {
    return v1.PodQOSGuaranteed
  }
  return v1.PodQOSBurstable
}

// github/kubernetes/pkg/kubelet/qos/policy.go
const (
  // KubeletOOMScoreAdj is the OOM score adjustment for Kubelet
  KubeletOOMScoreAdj int = -999
  // KubeProxyOOMScoreAdj is the OOM score adjustment for kube-proxy
  KubeProxyOOMScoreAdj  int = -999
  guaranteedOOMScoreAdj int = -997
  besteffortOOMScoreAdj int = 1000
)
func GetContainerOOMScoreAdjust(pod *v1.Pod, container *v1.Container, memoryCapacity int64) int {
  // 高优先级 Pod 直接返回 guaranteedOOMScoreAdj
  if types.IsCriticalPod(pod) {
    // Critical pods should be the last to get killed.
    return guaranteedOOMScoreAdj
  }
  // 根据 QoS 等级，返回 guaranteedOOMScoreAdj 或 besteffortOOMScoreAdj 的分数，这里只处理 Guaranteed 与 BestEffort
  switch v1qos.GetPodQOS(pod) {
  case v1.PodQOSGuaranteed:
    // Guaranteed containers should be the last to get killed.
    return guaranteedOOMScoreAdj
  case v1.PodQOSBestEffort:
    return besteffortOOMScoreAdj
  }
  memoryRequest := container.Resources.Requests.Memory().Value()
  // 内存占用越少，分数越高
  oomScoreAdjust := 1000 - (1000*memoryRequest)/memoryCapacity
  // 保证 Burstable 分数高于 Guaranteed
  if int(oomScoreAdjust) < (1000 + guaranteedOOMScoreAdj) {
    return (1000 + guaranteedOOMScoreAdj)
  }
  // 保证 Burstable 分数低于 BestEffect
  if int(oomScoreAdjust) == besteffortOOMScoreAdj {
    return int(oomScoreAdjust - 1)
  }
  return int(oomScoreAdjust)
}