Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752125AbbGIONb (ORCPT ); Thu, 9 Jul 2015 10:13:31 -0400 Received: from mail-wg0-f50.google.com ([74.125.82.50]:33364 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751341AbbGIONY (ORCPT ); Thu, 9 Jul 2015 10:13:24 -0400 Date: Thu, 9 Jul 2015 16:13:21 +0200 From: Michal Hocko To: Vladimir Davydov Cc: Johannes Weiner , Andrew Morton , Tejun Heo , Oleg Nesterov , Greg Thelen , KAMEZAWA Hiroyuki , KOSAKI Motohiro , linux-mm@kvack.org, LKML Subject: Re: [PATCH 8/8] memcg: get rid of mem_cgroup_from_task Message-ID: <20150709141320.GH13872@dhcp22.suse.cz> References: <1436358472-29137-1-git-send-email-mhocko@kernel.org> <1436358472-29137-9-git-send-email-mhocko@kernel.org> <20150708174331.GH2436@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150708174331.GH2436@esperanza> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1482 Lines: 40 On Wed 08-07-15 20:43:31, Vladimir Davydov wrote: > On Wed, Jul 08, 2015 at 02:27:52PM +0200, Michal Hocko wrote: [...] > > @@ -1091,12 +1079,14 @@ bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg) > > task_unlock(p); > > } else { > > /* > > - * All threads may have already detached their mm's, but the oom > > - * killer still needs to detect if they have already been oom > > - * killed to prevent needlessly killing additional tasks. > > + * All threads have already detached their mm's but we should > > + * still be able to at least guess the original memcg from the > > + * task_css. These two will match most of the time but there are > > + * corner cases where task->mm and task_css refer to a different > > + * cgroups. > > */ > > rcu_read_lock(); > > - task_memcg = mem_cgroup_from_task(task); > > + task_memcg = mem_cgroup_from_css(task_css(task, memory_cgrp_id)); > > css_get(&task_memcg->css); > > I wonder why it's safe to call css_get here. What do you mean by safe? Memcg cannot go away because we are under rcu lock. > > The patch itself looks good though, > > Reviewed-by: Vladimir Davydov Thanks! -- 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/