From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id C38B56B024D for ; Tue, 27 Jul 2010 23:10:59 -0400 (EDT) Date: Tue, 27 Jul 2010 23:10:49 -0400 From: Vivek Goyal Subject: Re: [RFC][PATCH 2/7][memcg] cgroup arbitarary ID allocation Message-ID: <20100728031049.GF12642@redhat.com> References: <20100727165155.8b458b7f.kamezawa.hiroyu@jp.fujitsu.com> <20100727165417.dacbe199.kamezawa.hiroyu@jp.fujitsu.com> <20100728023027.GD12642@redhat.com> <20100728113529.f086716d.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100728113529.f086716d.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "nishimura@mxp.nes.nec.co.jp" , "balbir@linux.vnet.ibm.com" , gthelen@google.com, m-ikeda@ds.jp.nec.com, "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" List-ID: On Wed, Jul 28, 2010 at 11:35:29AM +0900, KAMEZAWA Hiroyuki wrote: > On Tue, 27 Jul 2010 22:30:27 -0400 > Vivek Goyal wrote: > > > > Index: mmotm-2.6.35-0719/Documentation/cgroups/cgroups.txt > > > =================================================================== > > > --- mmotm-2.6.35-0719.orig/Documentation/cgroups/cgroups.txt > > > +++ mmotm-2.6.35-0719/Documentation/cgroups/cgroups.txt > > > @@ -621,6 +621,15 @@ and root cgroup. Currently this will onl > > > the default hierarchy (which never has sub-cgroups) and a hierarchy > > > that is being created/destroyed (and hence has no sub-cgroups). > > > > > > +void custom_id(struct cgroup_subsys *ss, struct cgroup *cgrp) > > > + > > > +Called at assigning a new ID to cgroup subsystem state struct. This > > > +is called when ss->use_id == true. If this function is not provided, > > > +a new ID is automatically assigned. If you enable ss->use_id, > > > +you can use css_lookup() and css_get_next() to access "css" objects > > > +via IDs. > > > + > > > > Couple of lines to explain why a subsystem would like to assign its > > own ids and not be happy with generic cgroup assigned id be helpful. > > In this case, I think you are using this id as index into array > > and want to control the index, hence you seem to be doing it. > > > > But I am not sure again why do you want to control index? > > > > Now, the subsystem allocation/id-allocation order is > > ->create() > alloc_id. > > Otherwise "id" of memory cgroup is just determined by the place in virtual-indexed > array. > As > memcg = mem_cgroup_base + id > > This "id" is determined at create(). > > If "id" is determined regardless of memory cgroup's placement, it's of no use. > My original design of css_id() allocates id in create() but it was moved to > generic part. So, this is expected change in my plan. > > We have 2 choices. > id = alloc_id() > create(id) > or > this patch. > > Both are okay for me. But alloc id before create() may add some ugly rollback. Ok, so in current design at the time of mem_cgroup instantiation css_id is not available so you don't know at what index to put the newly instantiated mem_cgroup object, hence the notion of let subsys decide the css_id and cgroup can query from subsystem later. I don't have any preference. Anything simple works.. Vivek -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org