[jira] [Commented] (YARN-6757) Refactor the usage of yarn.nodemanager.linux-container-executor.cgroups.mount-path

["Daniel Templeton (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/YARN-6757?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16075459#comment-16075459 ] 

Daniel Templeton commented on YARN-6757:
----------------------------------------

Thanks for the patch, [~miklos.szegedi@cloudera.com].  A few comments:

# The javadoc description for {{CGroupsHandler.getValidCGroups()}} should end with a period.
# {{CGroupsHandler.getValidCGroups()}} seems altogether unnecessary.  It's really just doing {{new HashSet<>(Arrays.asList(CGroupsController.values()))}} long hand.  Maybe even better would be to use an {{EnumSet}} instead of a {{HashSet}}.
# In {checkConfiguredCGroupPath()}}, {{cGroupMountPathSpecified}} is a little long-winded.  {{cGroupMountPath}} is plenty.
# {{checkConfiguredCGroupPath()}} isn't a great name.  Maybe {{loadConfiguredCGroupPath()}} or {{parseConfiguredCGroupPath}}?
# Why does {{CgroupsLCEResourcesHandler}} have an identical copy of {{checkConfiguredCGroupPath()}}?  Seems like there should be some code sharing...
# Theres now a dead import in {{CgroupsLCEResourcesHandler}}.
# What's with the mount path containing directories that contain files whose names are comma-separated lists or cgroups?  Is that a normal cgroups thing?  Sounds weird to me...
# I love that the text in {{yarn-defaults.xml}} is detailed and prescriptive, but it needs some work.  There are grammar issues, but first let's tackle the clarity issues.  I don't know what it's trying to say.  I get that the property sets a path that we'll use to resolve cgroups under certain circumstances, but it's not clear what those circumstances are and what will happen when this property is set.  It also says nothing about the file names that are comma-separated lists of cgroups.  If it helps, I'm happy to have an offline conversation and help craft the docs.

> Refactor the usage of yarn.nodemanager.linux-container-executor.cgroups.mount-path
> ----------------------------------------------------------------------------------
>
>                 Key: YARN-6757
>                 URL: https://issues.apache.org/jira/browse/YARN-6757
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: nodemanager
>    Affects Versions: 3.0.0-alpha4
>            Reporter: Miklos Szegedi
>            Assignee: Miklos Szegedi
>            Priority: Minor
>         Attachments: YARN-6757.000.patch
>
>
> We should add the ability to specify a custom cgroup path. This is how the documentation of {{linux-container-executor.cgroups.mount-path}} would look like:
> {noformat}
>     Requested cgroup mount path. Yarn has built in functionality to discover
>     the system cgroup mount paths, so use this setting only, if the discovery does not work.
>     This path must exist before the NodeManager is launched.
>     The location can vary depending on the Linux distribution in use.
>     Common locations include /sys/fs/cgroup and /cgroup.
>     If cgroups are not mounted, set yarn.nodemanager.linux-container-executor.cgroups.mount
>     to true. In this case it specifies, where the LCE should attempt to mount cgroups if not found.
>     If cgroups is accessible through lxcfs or some other file system,
>     then set this path and yarn.nodemanager.linux-container-executor.cgroups.mount to false.
>     Yarn tries to use this path first, before any cgroup mount point discovery.
>     If it cannot find this directory, it falls back to searching for cgroup mount points in the system.
>     Only used when the LCE resources handler is set to the CgroupsLCEResourcesHandler
> {noformat}



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