linux-kernel - Re: [PATCH] cgroup: add tracepoints to track cgroup events

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Message-ID: <20140821170002.GB7625@Dell>
Date:	Thu, 21 Aug 2014 11:00:02 -0600
From:	Andrea Righi <andrea@...terlinux.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Li Zefan <lizefan@...wei.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Matt Heaton <matt@...terlinux.com>
Subject: Re: [PATCH] cgroup: add tracepoints to track cgroup events

On Thu, Aug 21, 2014 at 09:35:41AM -0600, Andrea Righi wrote:
> On Thu, Aug 21, 2014 at 09:13:30AM -0500, Tejun Heo wrote:
> > Hello,
> > 
> > On Wed, Aug 20, 2014 at 09:46:25PM -0600, Andrea Righi wrote:
> > > This patch adds the following tracepoints:
> > >  o trace_cgroup_create       when a new cgroup is created
> > >  o trace_cgroup_destroy      when a cgroup is removed
> > >  o trace_cgroup_task_migrate when a task/thread is moved from a cgroup to another
> > > 
> > > The purpose of these tracepoints is to identify and help cgroup "managers" to
> > > diagnose problems and detect when they are doing an excessive amount of work.
> > 
> > Using TPs for this looks like a really roundabout way of doing this
> > when the whole interface is based on filesystem.  Extending
> > kernfs_notity to support directory events seems like a better way to
> > do this.
> > 
> > Thanks.
> > 
> > -- 
> > tejun
> 
> Agreed. Thanks for the suggestion, Tejun.
> 
> -Andrea

hmm... am I missing something or we already support directory events?

Example:

root@...l:~# grep cgroups /proc/mounts
none /cgroups cgroup rw,relatime,cpuset,cpu,cpuacct,memory,devices,freezer,perf_event,hugetlb 0 0
root@...l:~# inotifywait -m -r -e modify -e move -e create -e delete /cgroups
Setting up watches.  Beware: since -r was given, this may take a while!
Watches established.
/cgroups/ CREATE,ISDIR test
/cgroups/test/ MODIFY cgroup.procs
/cgroups/test/ MODIFY cgroup.procs
/cgroups/test/ MODIFY cgroup.populated
/cgroups/ MODIFY cgroup.procs
/cgroups/ MODIFY cgroup.procs
/cgroups/test/ MODIFY cgroup.populated
/cgroups/ DELETE,ISDIR test

I still need to figure out a smart way to track which PIDs are
added/removed to/from cgroup.procs from userland (inotifywait + git? :)),
but all the other informations provided by my tracepoint patch seem to
be already available via [di]notify.

Thanks,
-Andrea
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