The settings I have (on my very small experimental boxes) in my yarn-site.xml:

<property>
  <name>yarn.nodemanager.resource.memory-mb</name>
  <value>2200</value>
  <description>Amount of physical memory, in MB, that can be allocated for containers.</description>
</property>

<property>
  <name>yarn.scheduler.minimum-allocation-mb</name>
  <value>500</value>
</property>