From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752721AbaBJOlz (ORCPT ); Mon, 10 Feb 2014 09:41:55 -0500 Received: from mail-wg0-f42.google.com ([74.125.82.42]:38865 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752074AbaBJOlv (ORCPT ); Mon, 10 Feb 2014 09:41:51 -0500 Date: Mon, 10 Feb 2014 15:41:48 +0100 From: Michal Hocko To: Johannes Weiner Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 6/8] memcg: get_mem_cgroup_from_mm() Message-ID: <20140210144148.GK7117@dhcp22.suse.cz> References: <1391792665-21678-1-git-send-email-hannes@cmpxchg.org> <1391792665-21678-7-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1391792665-21678-7-git-send-email-hannes@cmpxchg.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 07-02-14 12:04:23, Johannes Weiner wrote: > Instead of returning NULL from try_get_mem_cgroup_from_mm() when the > mm owner is exiting, just return root_mem_cgroup. This makes sense > for all callsites and gets rid of some of them having to fallback > manually. It makes sense now that css reference counting is basically for free so we do not have to prevent reference counting on the root. > Signed-off-by: Johannes Weiner Acked-by: Michal Hocko > --- > mm/memcontrol.c | 18 ++++-------------- > 1 file changed, 4 insertions(+), 14 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 689fffdee471..37946635655c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1071,7 +1071,7 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p) > return mem_cgroup_from_css(task_css(p, mem_cgroup_subsys_id)); > } > > -struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm) > +struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) > { > struct mem_cgroup *memcg = NULL; > > @@ -1079,7 +1079,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm) > do { > memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); > if (unlikely(!memcg)) > - break; > + memcg = root_mem_cgroup; > } while (!css_tryget(&memcg->css)); > rcu_read_unlock(); > return memcg; > @@ -1475,7 +1475,7 @@ bool task_in_mem_cgroup(struct task_struct *task, > > p = find_lock_task_mm(task); > if (p) { > - curr = try_get_mem_cgroup_from_mm(p->mm); > + curr = get_mem_cgroup_from_mm(p->mm); > task_unlock(p); > } else { > /* > @@ -1489,8 +1489,6 @@ bool task_in_mem_cgroup(struct task_struct *task, > css_get(&curr->css); > rcu_read_unlock(); > } > - if (!curr) > - return false; > /* > * We should check use_hierarchy of "memcg" not "curr". Because checking > * use_hierarchy of "curr" here make this function true if hierarchy is > @@ -3649,15 +3647,7 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order) > if (!current->mm || current->memcg_kmem_skip_account) > return true; > > - memcg = try_get_mem_cgroup_from_mm(current->mm); > - > - /* > - * very rare case described in mem_cgroup_from_task. Unfortunately there > - * isn't much we can do without complicating this too much, and it would > - * be gfp-dependent anyway. Just let it go > - */ > - if (unlikely(!memcg)) > - return true; > + memcg = get_mem_cgroup_from_mm(current->mm); > > if (!memcg_can_account_kmem(memcg)) { > css_put(&memcg->css); > -- > 1.8.5.3 > -- Michal Hocko SUSE Labs