Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1768249Ab2KOPM7 (ORCPT ); Thu, 15 Nov 2012 10:12:59 -0500 Received: from cantor2.suse.de ([195.135.220.15]:44962 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1768148Ab2KOPM6 (ORCPT ); Thu, 15 Nov 2012 10:12:58 -0500 Date: Thu, 15 Nov 2012 16:12:55 +0100 From: Michal Hocko To: Tejun Heo Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, KAMEZAWA Hiroyuki , Johannes Weiner , Ying Han , Glauber Costa Subject: Re: [RFC 2/5] memcg: rework mem_cgroup_iter to use cgroup iterators Message-ID: <20121115151255.GE11990@dhcp22.suse.cz> References: <1352820639-13521-1-git-send-email-mhocko@suse.cz> <1352820639-13521-3-git-send-email-mhocko@suse.cz> <20121113161442.GA18227@mtj.dyndns.org> <20121114085129.GC17111@dhcp22.suse.cz> <20121114185245.GF21185@mtj.dyndns.org> <20121115095103.GB11990@dhcp22.suse.cz> <20121115144732.GB7306@mtj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121115144732.GB7306@mtj.dyndns.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2021 Lines: 45 On Thu 15-11-12 06:47:32, Tejun Heo wrote: > Hello, Michal. > > On Thu, Nov 15, 2012 at 10:51:03AM +0100, Michal Hocko wrote: > > > I'm a bit confused. Why would that make any difference? Shouldn't it > > > be just able to test the condition and continue? > > > > Ohh, I misunderstood your proposal. So what you are suggesting is > > to put all the logic we have in mem_cgroup_iter inside what you call > > reclaim here + mem_cgroup_iter_break inside the loop, right? > > > > I do not see how this would help us much. mem_cgroup_iter is not the > > nicest piece of code but it handles quite a complex requirements that we > > have currently (css reference count, multiple reclaimers racing). So I > > would rather keep it this way. Further simplifications are welcome of > > course. > > > > Is there any reason why you are not happy about direct using of > > cgroup_next_descendant_pre? > > Because I'd like to consider the next functions as implementation > detail, and having interations structred as loops tend to read better > and less error-prone. e.g. when you use next functions directly, it's > way easier to circumvent locking requirements in a way which isn't > very obvious. The whole point behind mem_cgroup_iter is to hide all the complexity behind memcg iteration. Memcg code either use for_each_mem_cgroup_tree for !reclaim case and mem_cgroup_iter otherwise. > So, unless it messes up the code too much (and I can't see why it > would), I'd much prefer if memcg used for_each_*() macros. As I said this would mean that the current mem_cgroup_iter code would have to be inverted which doesn't simplify the code much. I'd rather hide all the grossy details inside the memcg iterator. Or am I still missing your suggestion? -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/