From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f179.google.com (mail-pd0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id A06556B0253 for ; Sat, 11 Jul 2015 03:09:20 -0400 (EDT) Received: by pdjr16 with SMTP id r16so34403697pdj.3 for ; Sat, 11 Jul 2015 00:09:20 -0700 (PDT) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id pw8si18059395pdb.85.2015.07.11.00.09.19 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 11 Jul 2015 00:09:19 -0700 (PDT) Date: Sat, 11 Jul 2015 10:09:06 +0300 From: Vladimir Davydov Subject: Re: [PATCH 7/8] memcg: get rid of mm_struct::owner Message-ID: <20150711070905.GO2436@esperanza> 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> <20150710124520.GA29540@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20150710124520.GA29540@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Johannes Weiner , Andrew Morton , Tejun Heo , Oleg Nesterov , Greg Thelen , KAMEZAWA Hiroyuki , KOSAKI Motohiro , linux-mm@kvack.org, LKML On Fri, Jul 10, 2015 at 02:45:20PM +0200, Michal Hocko wrote: > 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. Why can't we make root_mem_cgroup statically allocated? AFAICS it's a common practice - e.g. see blkcg_root, root_task_group. Thanks, Vladimir -- 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