linux-kernel - Re: [PATCH v1 3/3] cgroup: relax common ancestor restriction for direct descendants

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Message-ID: <20160721152648.GA23759@htj.duckdns.org>
Date:	Thu, 21 Jul 2016 11:26:48 -0400
From:	Tejun Heo <tj@...nel.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Aleksa Sarai <asarai@...e.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Aditya Kali <adityakali@...gle.com>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Christian Brauner <cbrauner@...e.de>, dev@...ncontainers.org
Subject: Re: [PATCH v1 3/3] cgroup: relax common ancestor restriction for
 direct descendants

Hello, James.

On Thu, Jul 21, 2016 at 08:16:34AM -0700, James Bottomley wrote:
> > That'd be one side.  The other side is the one moving.  Let's say the
> > system admin thing wants to move all processe from A proper to B.  It
> > would do that by draining processes from A's procs file into B's and
> > even that is multistep and can race.
> 
> So the second part is that once we allow the creation of
> subdirectories, there's no unified tasks file, so there's no way of
> draining A proper without enumerating and descending into the cgroupns
> created subtrees in A?

Not that.  If it races, it will end up moving processes which are no
longer in A proper.  Such operations or distinctions might not be
meaningful under many circumstances but it'd be a pretty big hole in
the API to create and I can't really declare these holes are gonna be
okay with confidence.

Thanks.

-- 
tejun