Commit 7823da36 authored by Paul Menage's avatar Paul Menage Committed by Linus Torvalds
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cgroups: update documentation of cgroups tasks and procs files

Update documentation of cgroups tasks and procs files

Document the cgroup.procs file.

Clarify the semantics of the cgroup.procs and tasks files.  Although the
current cgroup.procs interface returns a sorted and uniqified list of
pids, potential future performance enhancements could result in those
properties being removed - explicitly document this aspect of the API.

There are no existing users of cgroup.procs, so compatibility isn't an
issue.  There are users of the "tasks" file, but none that would appear to
break in the event of the sorted property being broken.  The standard
"libcpuset" explicitly sorts the results of reading from the tasks file,
and "libcg" and other users don't appear to care about ordering.

Signed-off-by: default avatarPaul Menage <>
Reviewed-by: default avatarLi Zefan <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 06d1baa6
......@@ -227,7 +227,14 @@ as the path relative to the root of the cgroup file system.
Each cgroup is represented by a directory in the cgroup file system
containing the following files describing that cgroup:
- tasks: list of tasks (by pid) attached to that cgroup
- tasks: list of tasks (by pid) attached to that cgroup. This list
is not guaranteed to be sorted. Writing a thread id into this file
moves the thread into this cgroup.
- cgroup.procs: list of tgids in the cgroup. This list is not
guaranteed to be sorted or free of duplicate tgids, and userspace
should sort/uniquify the list if this property is required.
Writing a tgid into this file moves all threads with that tgid into
this cgroup.
- notify_on_release flag: run the release agent on exit?
- release_agent: the path to use for release notifications (this file
exists in the top cgroup only)
......@@ -374,7 +381,7 @@ Now you want to do something with this cgroup.
In this directory you can find several files:
# ls
notify_on_release tasks
cgroup.procs notify_on_release tasks
(plus whatever files added by the attached subsystems)
Now attach your shell to this cgroup:
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