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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2016-10-07 22:19:46 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2016-10-08 14:08:23 +0200 |
| commit | 754f4cf5bdbe04b5d5f5de06aeb842793bdab42a (patch) | |
| tree | 270b2140b79db69855bf6e6fed37770d520e345c /man7/cgroups.7 | |
| parent | dddb7ea1fc7160f4decc933b76cfa611951dc037 (diff) | |
| download | man-pages-754f4cf5bdbe04b5d5f5de06aeb842793bdab42a.tar.gz | |
cgroups.7: Describe the cgroups v2 cgroup.events file
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man7/cgroups.7')
| -rw-r--r-- | man7/cgroups.7 | 57 |
1 files changed, 46 insertions, 11 deletions
diff --git a/man7/cgroups.7 b/man7/cgroups.7 index 531d3bb9c5..cff1ac5fb4 100644 --- a/man7/cgroups.7 +++ b/man7/cgroups.7 @@ -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 |