From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx149.postini.com [74.125.245.149]) by kanga.kvack.org (Postfix) with SMTP id 281256B0095 for ; Tue, 11 Dec 2012 17:36:11 -0500 (EST) Received: by mail-pb0-f41.google.com with SMTP id xa7so3140015pbc.14 for ; Tue, 11 Dec 2012 14:36:10 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20121211155432.GC1612@dhcp22.suse.cz> References: <1353955671-14385-1-git-send-email-mhocko@suse.cz> <1353955671-14385-4-git-send-email-mhocko@suse.cz> <20121211155432.GC1612@dhcp22.suse.cz> Date: Tue, 11 Dec 2012 14:36:10 -0800 Message-ID: Subject: Re: [patch v2 3/6] memcg: rework mem_cgroup_iter to use cgroup iterators From: Ying Han Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, KAMEZAWA Hiroyuki , Johannes Weiner , Tejun Heo , Glauber Costa , Li Zefan On Tue, Dec 11, 2012 at 7:54 AM, Michal Hocko wrote: > On Sun 09-12-12 11:39:50, Ying Han wrote: >> On Mon, Nov 26, 2012 at 10:47 AM, Michal Hocko wrote: > [...] >> > if (reclaim) { >> > - iter->position = id; >> > + struct mem_cgroup *curr = memcg; >> > + >> > + if (last_visited) >> > + css_put(&last_visited->css); > ^^^^^^^^^^^ > here >> > + >> > + if (css && !memcg) >> > + curr = mem_cgroup_from_css(css); >> > + >> > + /* make sure that the cached memcg is not removed */ >> > + if (curr) >> > + css_get(&curr->css); >> > + iter->last_visited = curr; >> >> Here we take extra refcnt for last_visited, and assume it is under >> target reclaim which then calls mem_cgroup_iter_break() and we leaked >> a refcnt of the target memcg css. > > I think you are not right here. The extra reference is kept for > iter->last_visited and it will be dropped the next time somebody sees > the same zone-priority iter. See above. > > Or have I missed your question? Hmm, question remains. My understanding of the mem_cgroup_iter() is that each call path should close the loop itself, in the sense that no *leaked* css refcnt after that loop finished. It is the case for all the caller today where the loop terminates at memcg == NULL, where all the refcnt have been dropped by then. One exception is mem_cgroup_iter_break(), where the loop terminates with *leaked* refcnt and that is what the iter_break() needs to clean up. We can not rely on the next caller of the loop since it might never happen. It makes sense to drop the refcnt of last_visited, the same reason as drop refcnt of prev. I don't see why it makes different. --Ying > > [...] > -- > Michal Hocko > SUSE Labs -- 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