From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3300C76195 for ; Thu, 18 Jul 2019 09:31:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5A1D20665 for ; Thu, 18 Jul 2019 09:31:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389708AbfGRJbI (ORCPT ); Thu, 18 Jul 2019 05:31:08 -0400 Received: from relay.sw.ru ([185.231.240.75]:54274 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727474AbfGRJbI (ORCPT ); Thu, 18 Jul 2019 05:31:08 -0400 Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.92) (envelope-from ) id 1ho2ke-0005VV-9n; Thu, 18 Jul 2019 12:31:00 +0300 Subject: Re: [PATCH] mm: vmscan: check if mem cgroup is disabled or not before calling memcg slab shrinker To: Yang Shi , shakeelb@google.com, vdavydov.dev@gmail.com, hannes@cmpxchg.org, mhocko@suse.com, guro@fb.com, hughd@google.com, cai@lca.pw, kirill.shutemov@linux.intel.com, akpm@linux-foundation.org Cc: stable@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1563385526-20805-1-git-send-email-yang.shi@linux.alibaba.com> From: Kirill Tkhai Message-ID: Date: Thu, 18 Jul 2019 12:30:49 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <1563385526-20805-1-git-send-email-yang.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.07.2019 20:45, Yang Shi wrote: > Shakeel Butt reported premature oom on kernel with > "cgroup_disable=memory" since mem_cgroup_is_root() returns false even > though memcg is actually NULL. The drop_caches is also broken. > > It is because commit aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() > calls in shrink_node()") removed the !memcg check before > !mem_cgroup_is_root(). And, surprisingly root memcg is allocated even > though memory cgroup is disabled by kernel boot parameter. > > Add mem_cgroup_disabled() check to make reclaimer work as expected. > > Fixes: aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in shrink_node()") > Reported-by: Shakeel Butt > Cc: Vladimir Davydov > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Kirill Tkhai > Cc: Roman Gushchin > Cc: Hugh Dickins > Cc: Qian Cai > Cc: Kirill A. Shutemov > Cc: stable@vger.kernel.org 4.19+ > Signed-off-by: Yang Shi Reviewed-by: Kirill Tkhai Surprise really. We have mem_cgroup as not early inited, so all of these boundary cases and checks has to be supported. But it looks like it's not possible to avoid that in any way. > --- > mm/vmscan.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f8e3dcd..c10dc02 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -684,7 +684,14 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, > unsigned long ret, freed = 0; > struct shrinker *shrinker; > > - if (!mem_cgroup_is_root(memcg)) > + /* > + * The root memcg might be allocated even though memcg is disabled > + * via "cgroup_disable=memory" boot parameter. This could make > + * mem_cgroup_is_root() return false, then just run memcg slab > + * shrink, but skip global shrink. This may result in premature > + * oom. > + */ > + if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) > return shrink_slab_memcg(gfp_mask, nid, memcg, priority); > > if (!down_read_trylock(&shrinker_rwsem)) >