There are 4 files refering to NodeManager under hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/markdown.
NodeManagerCgroups.md: It is not the doc about NodeManager and just the file name is not appropiate. It explains about feature supported by LinuxContainerExecutor only. Even if CGroups is supported by other modules in future, it might not be speficic to NodeManager.
NodeManagerRest.md: This is relatively big and reasonable to be independent page same as other REST API docs.