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cgroups.7: Describe the cgroups v2 cgroup.events file 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk 2016-10-07 22:19:46 +02:00
parent dddb7ea1fc
commit 754f4cf5bd
1 changed files with 46 additions and 11 deletions
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man7/cgroups.7
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@ -549,17 +549,52 @@ controller is not enabled in
then it cannot be enabled in
.IR /A/B/C .
.\"
.SS Cgroups v2 events file
.\" FIXME The following text is wrong
A new feature in cgroups v2 is the
.I cgroup.populated
file.
This reads 0 if there are no processes in the cgroup or its descendants,
and 1 otherwise.
It can be watched for changes using
.BR inotify (7).
This allows user-space applications to efficiently watch cgroups
for autoremove conditions.
.SS Cgroups v2 cgroup.events file
With cgroups v2, a new mechanism is provided to obtain notification
about when a cgroup becomes empty.
The cgroups v1
.IR release_agent
and
.IR notify_on_release
files are removed, and replaced by a new, more general-purpose file,
.IR cgroup.events .
This file contains key-value pairs
(delimited by newline characters, with the key and value separated by spaces)
that identify events or state for a cgroup.
Currently, only one key appears in this file,
.IR populated ,
which has either the value 0,
meaning that the cgroup (and its descendants)
contain no (nonzombie) processes,
or 1, meaning that the cgroup contains member processes.
The
.IR cgroup.events
file can be monitored, in order to receive notification when a cgroup
transitions between the populated and unpopulated states (or vice versa).
When monitoring this file using
.BR inotify (7),
transitions generate
.BR IN_MODIFY
events, and when monitoring the file using
.BR poll (2),
transitions generate
.B POLLPRI
events.
The cgroups v2
.IR notify_on_release
mechanism offers at least two advantages over the cgroups v1
.IR release_agent
mechanism.
First, it allows for cheaper notification,
since a single process can monitor multiple
.IR cgroup.events
files.
By contrast, the cgroups v1 mechanism requires the creation
of a process for each notification.
Second, notfication can be delegated to a process that lives inside
a container associated with the newly empty cgroup.
.\"
.SS /proc files
.TP