From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx140.postini.com [74.125.245.140]) by kanga.kvack.org (Postfix) with SMTP id 46F386B005D for ; Fri, 12 Oct 2012 04:41:03 -0400 (EDT) Date: Fri, 12 Oct 2012 10:41:01 +0200 From: Michal Hocko Subject: Re: [PATCH v4 09/14] memcg: kmem accounting lifecycle management Message-ID: <20121012084100.GE10110@dhcp22.suse.cz> References: <1349690780-15988-1-git-send-email-glommer@parallels.com> <1349690780-15988-10-git-send-email-glommer@parallels.com> <20121011131143.GF29295@dhcp22.suse.cz> <5077CB05.907@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5077CB05.907@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Mel Gorman , Suleiman Souhlal , Tejun Heo , cgroups@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, Johannes Weiner , Greg Thelen , devel@openvz.org, Frederic Weisbecker , Christoph Lameter , Pekka Enberg On Fri 12-10-12 11:47:17, Glauber Costa wrote: > On 10/11/2012 05:11 PM, Michal Hocko wrote: > > On Mon 08-10-12 14:06:15, Glauber Costa wrote: > >> Because kmem charges can outlive the cgroup, we need to make sure that > >> we won't free the memcg structure while charges are still in flight. > >> For reviewing simplicity, the charge functions will issue > >> mem_cgroup_get() at every charge, and mem_cgroup_put() at every > >> uncharge. > >> > >> This can get expensive, however, and we can do better. mem_cgroup_get() > >> only really needs to be issued once: when the first limit is set. In the > >> same spirit, we only need to issue mem_cgroup_put() when the last charge > >> is gone. > >> > >> We'll need an extra bit in kmem_accounted for that: KMEM_ACCOUNTED_DEAD. > >> it will be set when the cgroup dies, if there are charges in the group. > >> If there aren't, we can proceed right away. > >> > >> Our uncharge function will have to test that bit every time the charges > >> drop to 0. Because that is not the likely output of > >> res_counter_uncharge, this should not impose a big hit on us: it is > >> certainly much better than a reference count decrease at every > >> operation. > >> > >> [ v3: merged all lifecycle related patches in one ] > >> > >> Signed-off-by: Glauber Costa > >> CC: Kamezawa Hiroyuki > >> CC: Christoph Lameter > >> CC: Pekka Enberg > >> CC: Michal Hocko > >> CC: Johannes Weiner > >> CC: Suleiman Souhlal > > > > OK, I like the optimization. I have just one comment to the > > memcg_kmem_dead naming but other than that > > > > Acked-by: Michal Hocko > > > > [...] > >> +static bool memcg_kmem_dead(struct mem_cgroup *memcg) > > > > The name is tricky because it doesn't tell you that it clears the flag > > which made me scratch my head when reading comment in kmem_cgroup_destroy > > > memcg_kmem_finally_kill_that_bastard() ? memcg_kmem_test_and_clear_dead? I know long but at least clear that the flag is cleared. Or just open code it. -- 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