Explanation
Label constraints can be used to schedule containers to meet the security policy requirements. Label constraints are expressions that match node labels to service labels. Node labels are key-value pairs that can be attached to nodes to identify them by certain characteristics, such as role, environment, region, etc. Service labels are key-value pairs that can be attached to services to specify scheduling preferences or requirements, such as node.role == manager or environment != production. Label constraints can be used with the
--constraint flag when creating or updating a service to ensure that the service's containers are scheduled on nodes that match the specified criteria. References:
https://docs.docker.com/engine/swarm/services/#specify-service-constraints,
https://docs.docker.com/engine/swarm/manage-nodes/#add-or-remove-label-metadata

Explanation
Resource reservation cannot be used to schedule containers to meet the security policy requirements, because resource reservation only affects the available resources on a node and does not restrict which containers can run on which nodes. According to the official documentation, resource reservation is used to ensure that a service has enough resources to run.
References: https://docs.docker.com/engine/swarm/services/#reserve-memory-or-cpus-for-a-service