Re: [RFC] cgroup basic comounting

[Glauber Costa]

On 12/19/2011 11:58 AM, Li Zefan wrote:
> Glauber Costa wrote:
> > Turns out that most of the infrastructure we need to put two controllers in the
> > same hierarchy is by far already into place. All we need to do is not failing
> > when we specify two of them.
>
> You don't need to change anything to mount with 2 cgroup subsystems:
>
> 	# mount -t cgroup -o cpu,cpuacct xxx /mnt
>
> But you may want to revise and make use of the subsys->bind() callback, which
> is called at mount/remount/umount when we attach/remove a controller to/from
> a hierarchy. It's the place you can check if two controllers are going to
> be comounted/seperated.
>
> > With this, we can effectively guarantee that by comounting cpu and cpuacct,
> > we'll have the same set of tasks, therefore allowing us to use cpu cgroup data
> > to fill in the usage fields in cpuacct.

Yeah, that patch was bogus, sorry for the noise.

What I should really have posted is the test code, but I guess I'll go 
over that one as well one more time, and then post it.

Thanks
> > I decided not to stabilish any dependency between cgroups as Li previously did:
> > cgroups may or may not be comounted, and any of them can be combined (I don't
> > see a reason to prevent any combination).
> >
> > After testing and some trials, I could verify that the current mount behavior
> > plays well under the plans, so I didn't change it. That is:
> >
> >   * If subsystems A and B aren't mounted, we can comount them.
> >   * If subsystem A is mounted, but B is not:
> >     * we can comount them if A has no children,
> >     * we fail otherwise
> >   * If subsystems A and B are comounted at a location, we can't
> >     mount any of them separately at another point. We do can mount
> >     them together.
> >   * If subsystems A and B are comounted at a location,
> >     * we can comount a third subsystem C, if they have no children
> >     * we fail otherwise
> >
> > Paul,
> >
> > Please let me know if this is tuned with the idea you had in mind.
> > If this is okay, I patch that extracts usage from cpu cgroup data
> > in case of comount would follow.
> >
> > Signed-off-by: Glauber Costa<glommer@xxxxxxxxxxxxx>
> > CC: Paul Turner<pjt@xxxxxxxxxx>
> > CC: Li Zefan<lizf@xxxxxxxxxxxxxx>
> > ---
> >   kernel/cgroup.c |    4 ++--
> >   1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> > index 1fd7867..e894a4f 100644
> > --- a/kernel/cgroup.c
> > +++ b/kernel/cgroup.c
> > @@ -1211,9 +1211,9 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
> >   			set_bit(i,&opts->subsys_bits);
> >   			one_ss = true;
> >
> > -			break;
> > +			continue;
> >   		}
> > -		if (i == CGROUP_SUBSYS_COUNT)
> > +		if (opts->subsys_bits == 0)
> >   			return -ENOENT;
> >   	}
> --
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