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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 5E636C4361B for ; Tue, 8 Dec 2020 17:15:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 34E0223B04 for ; Tue, 8 Dec 2020 17:15:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730694AbgLHROs (ORCPT ); Tue, 8 Dec 2020 12:14:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730009AbgLHROs (ORCPT ); Tue, 8 Dec 2020 12:14:48 -0500 Received: from mail-lj1-x241.google.com (mail-lj1-x241.google.com [IPv6:2a00:1450:4864:20::241]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C02D5C061749; Tue, 8 Dec 2020 09:14:01 -0800 (PST) Received: by mail-lj1-x241.google.com with SMTP id y16so20708371ljk.1; Tue, 08 Dec 2020 09:14:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=RUpZuflX/fflZb691Vksxu0oOE9kBri4IqZLX4977hA=; b=ToGq7tig3WXqleiJrdh4iBHR1FC6IaIV5nVE+7umT2hPvT2/L0mioUKcxhuREzcubc fNewEov5HtB3wzXZ9xfn8yIAVpo5uSg5yydxU4yjXZ5Qi277Q7JSpWOgYm04lq+Mufvl +7KtmAqC0hhBoIb/H/vo3iERYAffwTtucJjBrZhOBukoUwG03i2pOI5E9Mv6AY+EsKDy fR5D67+ylXTWijkVzFtkrx6T+a5EFezPbK0N4c0MHfYOHaOkftlWByQNY7GOUuUrI2On 1BObGECZcYeOzN/I6KiHrZnZF89XqbUJw5OF6K/Add2G1uttgzY6IRliPFEvHyEYGt4P wsTg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RUpZuflX/fflZb691Vksxu0oOE9kBri4IqZLX4977hA=; b=Y+msMn9Hk8M4AjvVNCJ1/47JX/iNhoxhXatTMhormckFME1RbJcQFQeHOg6jgp9WmI hDMH3TjtL+qQtVkQo0E+cfQ1N5Hc9y4Ws713Xk5YIbxTGWsiroohDZwyTzQiwQ/+B2BZ 77R2RRPsATCgUFMRdXWjrIGmuDcKVgWs53xUV2n6CGyUPJa7L4L/9HSAOYVKZXQn15EW 5PNl+L0BEfxvWHmJTJUxRzPQdE+TTiGWQiR8khjr1qOdsl2mxJHj7bFIoN9VIKXQPl7M cwvKX2P8Qq5UOwoBawq4fBmLJVujbkbWmZWOVusEeD7KbHEpv+FG5oah1gIIOQ6+6kcs zc5Q== X-Gm-Message-State: AOAM531S1b4r8kmUU4sp73mWBqX/V3xcmUQpRgzX1i9C5hv+ig7Rj584 BF9YKu26s/Zp1cllTc4TGUPX/zqnFC7riLt7d7C5ufsDIZ8= X-Google-Smtp-Source: ABdhPJx1cPCyxZJsBseFknmMFJytItPZ2gixASvcbkTzLl9+dE0kfoov9mNYZGtELWGQz6wvAQTtUcwmHPKF3oFjmg4= X-Received: by 2002:a2e:b4b3:: with SMTP id q19mr3689073ljm.121.1607447640230; Tue, 08 Dec 2020 09:14:00 -0800 (PST) MIME-Version: 1.0 References: <20201202182725.265020-1-shy828301@gmail.com> <20201202182725.265020-7-shy828301@gmail.com> <49464720-675d-5144-043c-eba6852a9c06@virtuozzo.com> In-Reply-To: <49464720-675d-5144-043c-eba6852a9c06@virtuozzo.com> From: Yang Shi Date: Tue, 8 Dec 2020 09:13:47 -0800 Message-ID: Subject: Re: [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker To: Kirill Tkhai Cc: Roman Gushchin , Shakeel Butt , Dave Chinner , Johannes Weiner , Michal Hocko , Andrew Morton , Linux MM , Linux FS-devel Mailing List , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 3, 2020 at 3:40 AM Kirill Tkhai wrote: > > 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. Sorry for the late reply, I don't know why Gmail filtered this out to spam. > > 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). It seems shrink_slab_memcg() might see shrinker_deferred as NULL either due to the same reason. I don't think there is a guarantee it won't happen. We just need guarantee CSS_ONLINE is seen after shrinker_maps and shrinker_deferred are allocated, so I'm supposed barriers before "css->flags |= CSS_ONLINE" should work. So the below patch may be ok: diff --git a/mm/memcontrol.c b/mm/memcontrol.c index df128cab900f..9f7fb0450d69 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5539,6 +5539,12 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) return -ENOMEM; } + /* + * Barrier for CSS_ONLINE, so that shrink_slab_memcg() sees shirnker_maps + * and shrinker_deferred before CSS_ONLINE. + */ + smp_mb(); + /* Online state pins memcg ID, memcg ID pins CSS */ refcount_set(&memcg->id.ref, 1); css_get(css); Or add one more check for shrinker_deferred sounds acceptable as well. > Kirill >