Pods stuck in pending with Insufficient memory while workers have free memory

Issue

• Pods are stuck in Pending state due to insufficient memory; An example of this error is provided below:

  0/6 nodes are available: 3 Insufficient memory, 3 node(s) had taint {node-role.kubernetes.io/master: }, that the pod didn't tolerate.
  

  When reviewing the Worker Nodes, it appears they have lots of available memory.

  $ oc adm top node
  NAME           CPU(cores)   CPU%   MEMORY(bytes)   MEMORY%
  worker1        2231m        11%    19831Mi         53%
  worker2        3459m        17%    32418Mi         87%
  worker3        6492m        33%    23469Mi         63%
  

  The Pod is requesting less than the available above, why is the Pod not be scheduled?

    - resources:
        limits:
          cpu: 500m
          memory: 500Mi
        requests:
          cpu: 500m
          memory: 500Mi
  

• Why are the oc adm top nodes and the oc describe nodes/<node-name> available resource values different?