From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f53.google.com (mail-wg0-f53.google.com [74.125.82.53]) by kanga.kvack.org (Postfix) with ESMTP id C94B36B0038 for ; Fri, 10 Jul 2015 08:45:25 -0400 (EDT) Received: by wgxm20 with SMTP id m20so65122640wgx.3 for ; Fri, 10 Jul 2015 05:45:25 -0700 (PDT) Received: from mail-wg0-f43.google.com (mail-wg0-f43.google.com. [74.125.82.43]) by mx.google.com with ESMTPS id c6si3272854wie.78.2015.07.10.05.45.23 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 10 Jul 2015 05:45:24 -0700 (PDT) Received: by wgjx7 with SMTP id x7so248230242wgj.2 for ; Fri, 10 Jul 2015 05:45:23 -0700 (PDT) Date: Fri, 10 Jul 2015 14:45:20 +0200 From: Michal Hocko Subject: Re: [PATCH 7/8] memcg: get rid of mm_struct::owner Message-ID: <20150710124520.GA29540@dhcp22.suse.cz> References: <1436358472-29137-1-git-send-email-mhocko@kernel.org> <1436358472-29137-8-git-send-email-mhocko@kernel.org> <20150708173251.GG2436@esperanza> <20150709140941.GG13872@dhcp22.suse.cz> <20150710075400.GN2436@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150710075400.GN2436@esperanza> Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Johannes Weiner , Andrew Morton , Tejun Heo , Oleg Nesterov , Greg Thelen , KAMEZAWA Hiroyuki , KOSAKI Motohiro , linux-mm@kvack.org, LKML On Fri 10-07-15 10:54:00, Vladimir Davydov wrote: > On Thu, Jul 09, 2015 at 04:09:41PM +0200, Michal Hocko wrote: > > On Wed 08-07-15 20:32:51, Vladimir Davydov wrote: > > > On Wed, Jul 08, 2015 at 02:27:51PM +0200, Michal Hocko wrote: > [...] > > > > @@ -474,7 +519,7 @@ static inline void mem_cgroup_count_vm_event(struct mm_struct *mm, > > > > return; > > > > > > > > rcu_read_lock(); > > > > - memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); > > > > + memcg = rcu_dereference(mm->memcg); > > > > if (unlikely(!memcg)) > > > > goto out; > > > > > > > > > > If I'm not mistaken, mm->memcg equals NULL for any task in the root > > > memory cgroup > > > > right > > > > > (BTW, it it's true, it's worth mentioning in the comment > > > to mm->memcg definition IMO). As a result, we won't account the stats > > > for such tasks, will we? > > > > well spotted! This is certainly a bug. There are more places which are > > checking for mm->memcg being NULL and falling back to root_mem_cgroup. I > > think it would be better to simply use root_mem_cgroup right away. We > > can setup init_mm.memcg = root_mem_cgroup during initialization and be > > done with it. What do you think? The diff is in the very end of the > > email (completely untested yet). > > I'd prefer initializing init_mm.memcg to root_mem_cgroup. This way we > wouldn't have to check whether mm->memcg is NULL or not here and there, > which would make the code cleaner IMO. So the patch I've posted will not work as a simple boot test told me. We are initializing root_mem_cgroup too late. This will be more complicated. I will leave this idea outside of this patch series and will come up with a separate patch which will clean this up later. I will update the doc discouraging any use of mm->memcg outside of memcg and use accessor functions instead. There is only one currently (mm/debug.c) and this is used only to print the pointer which is safe. -- 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