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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 CC066C64E8A for ; Thu, 3 Dec 2020 11:41:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7064F208FE for ; Thu, 3 Dec 2020 11:41:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388501AbgLCLlS (ORCPT ); Thu, 3 Dec 2020 06:41:18 -0500 Received: from relay.sw.ru ([185.231.240.75]:34248 "EHLO relay3.sw.ru" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726063AbgLCLlS (ORCPT ); Thu, 3 Dec 2020 06:41:18 -0500 Received: from [192.168.15.126] by relay3.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1kkmyH-00BZ31-6K; Thu, 03 Dec 2020 14:40:25 +0300 Subject: Re: [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker To: Yang Shi , guro@fb.com, shakeelb@google.com, david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20201202182725.265020-1-shy828301@gmail.com> <20201202182725.265020-7-shy828301@gmail.com> From: Kirill Tkhai Message-ID: <49464720-675d-5144-043c-eba6852a9c06@virtuozzo.com> Date: Thu, 3 Dec 2020 14:40:25 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201202182725.265020-7-shy828301@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02.12.2020 21:27, Yang Shi wrote: > Use per memcg's nr_deferred for memcg aware shrinkers. The shrinker's nr_deferred > will be used in the following cases: > 1. Non memcg aware shrinkers > 2. !CONFIG_MEMCG > 3. memcg is disabled by boot parameter > > Signed-off-by: Yang Shi > --- > mm/vmscan.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 82 insertions(+), 6 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index cba0bc8d4661..d569fdcaba79 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -203,6 +203,12 @@ static DECLARE_RWSEM(shrinker_rwsem); > static DEFINE_IDR(shrinker_idr); > static int shrinker_nr_max; > > +static inline bool is_deferred_memcg_aware(struct shrinker *shrinker) > +{ > + return (shrinker->flags & SHRINKER_MEMCG_AWARE) && > + !mem_cgroup_disabled(); > +} > + > static int prealloc_memcg_shrinker(struct shrinker *shrinker) > { > int id, ret = -ENOMEM; > @@ -271,7 +277,58 @@ static bool writeback_throttling_sane(struct scan_control *sc) > #endif > return false; > } > + > +static inline long count_nr_deferred(struct shrinker *shrinker, > + struct shrink_control *sc) > +{ > + bool per_memcg_deferred = is_deferred_memcg_aware(shrinker) && sc->memcg; > + struct memcg_shrinker_deferred *deferred; > + struct mem_cgroup *memcg = sc->memcg; > + int nid = sc->nid; > + int id = shrinker->id; > + long nr; > + > + if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) > + nid = 0; > + > + if (per_memcg_deferred) { > + deferred = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_deferred, > + true); My comment is about both 5/9 and 6/9 patches. shrink_slab_memcg() races with mem_cgroup_css_online(). A visibility of CSS_ONLINE flag in shrink_slab_memcg()->mem_cgroup_online() does not guarantee that you will see memcg->nodeinfo[nid]->shrinker_deferred != NULL in count_nr_deferred(). This may occur because of processor reordering on !x86 (there is no a common lock or memory barriers). Regarding to shrinker_map this is not a problem due to map check in shrink_slab_memcg(). The map can't be NULL there. Regarding to shrinker_deferred you should prove either this is not a problem too, or to add proper synchronization (maybe, based on barriers) or to add some similar check (maybe, in shrink_slab_memcg() too). Kirill