From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754123Ab3K2JpN (ORCPT ); Fri, 29 Nov 2013 04:45:13 -0500 Received: from mail-ea0-f171.google.com ([209.85.215.171]:57017 "EHLO mail-ea0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751210Ab3K2JpH (ORCPT ); Fri, 29 Nov 2013 04:45:07 -0500 Date: Fri, 29 Nov 2013 10:45:02 +0100 From: Michal Hocko To: Vladimir Davydov Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, devel@openvz.org, Johannes Weiner , Balbir Singh , KAMEZAWA Hiroyuki Subject: Re: [PATCH] memcg: fix kmem_account_flags check in memcg_can_account_kmem() Message-ID: <20131129094502.GD25893@dhcp22.suse.cz> References: <1385567162-14973-1-git-send-email-vdavydov@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1385567162-14973-1-git-send-email-vdavydov@parallels.com> 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 Wed 27-11-13 19:46:01, Vladimir Davydov wrote: > We should start kmem accounting for a memory cgroup only after both its > kmem limit is set (KMEM_ACCOUNTED_ACTIVE) and related call sites are > patched (KMEM_ACCOUNTED_ACTIVATED). This should be vice-versa, no? ACTIVE is set after static_key_slow_inc(&memcg_kmem_enabled_key) AFAICS. > Currently memcg_can_account_kmem() allows kmem accounting even if only > one of the conditions is true. > Fix it. It would be nice to describe, what is the actual problem here. I assume this is a charge vs. enable race. Let me try So we have KMEM_ACCOUNTED_ACTIVATED (set by memcg_update_cache_sizes) but the static key is not enabled yet (so KMEM_ACCOUNTED_ACTIVE is not set yet). memcg_can_account_kmem is called from 2 contexts during charge - memcg_kmem_get_cache via __memcg_kmem_get_cache - memcg_kmem_newpage_charge via __memcg_kmem_newpage_charge both of them start by checking memcg_kmem_enabled which is our static key before memcg_can_account_kmem. This would suggest that static_key+ACTIVE check memcg_can_account_kmem is sufficient. No? That being said the proposed change is not incorrect it just doesn't seem to _fix_ anything. I would much rather see a comprehensive documentation of the whole enabling workflow. E.g. why do we need ACTIVATED at all? Nobody seem to care in the code... > Signed-off-by: Vladimir Davydov > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Balbir Singh > Cc: KAMEZAWA Hiroyuki > --- > mm/memcontrol.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index f1a0ae6..40efb9d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2956,7 +2956,8 @@ static DEFINE_MUTEX(set_limit_mutex); > static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg) > { > return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) && > - (memcg->kmem_account_flags & KMEM_ACCOUNTED_MASK); > + (memcg->kmem_account_flags & KMEM_ACCOUNTED_MASK) == > + KMEM_ACCOUNTED_MASK; > } > > /* > -- > 1.7.10.4 > -- Michal Hocko SUSE Labs