From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [PATCH v2 6/6] blkcg, memcg: make blkcg depend on memcg on the default hierarchy Date: Wed, 9 Jul 2014 07:57:46 -0400 Message-ID: <20140709115746.GA26504@redhat.com> References: <1403917392-32555-1-git-send-email-tj@kernel.org> <1403917392-32555-7-git-send-email-tj@kernel.org> <20140628114907.GA10829@htj.dyndns.org> <20140708194226.GA18382@redhat.com> <20140708215351.GJ4979@htj.dyndns.org> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20140708215351.GJ4979-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo Cc: lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, mhocko-AlSwsSmVLrQ@public.gmane.org, axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org On Tue, Jul 08, 2014 at 05:53:51PM -0400, Tejun Heo wrote: > Hello, Vivek. > > On Tue, Jul 08, 2014 at 03:42:26PM -0400, Vivek Goyal wrote: > > I have couple questions about new semantics. Following is my > > understanding. Is it right? > > > > - So after this change one can not use blkio controller on unified > > hiearchy if memory controller is mounted on some other hierarchy > > and is not available for mounting unified hiearchy. > > Hmmm? No, the only behavior which changes is when both blkcg and > memcg are mounted on the unified hierarchy. Nothing else changes. > The dependency behavior kicks in iff memcg is available on the unified > hierarchy. Ok, good to know that dependency kicks in only if controlle being depended on is available on the hierarchy. > > > - If blkio controller is enabled on unified hiearchy (memory controller > > implicitly enabled), then one can't mount memory controller on other > > hierarchies without first disabling blkio controller on unified hiearchy. > > Yes, blkio needs to be disabled to the root for memcg to be able to > become free. This is an extra restriction but I don't think it's > anything drastic. Once a controller starts being actively used on any > hierarchy, nothing has been guaranteed about when the controller would > become free again even if the whole hierarchy is reduced to the root. Agreed. Thanks for the clarification. Thanks Vivek