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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 A2FF7C432BE for ; Mon, 2 Aug 2021 06:58:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5D004610A6 for ; Mon, 2 Aug 2021 06:58:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5D004610A6 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 97C616B005D; Mon, 2 Aug 2021 02:58:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 92CF56B006C; Mon, 2 Aug 2021 02:58:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 842708D0001; Mon, 2 Aug 2021 02:58:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0142.hostedemail.com [216.40.44.142]) by kanga.kvack.org (Postfix) with ESMTP id 6ECBA6B005D for ; Mon, 2 Aug 2021 02:58:02 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 42E7A8249980 for ; Mon, 2 Aug 2021 06:58:01 +0000 (UTC) X-FDA: 78429235962.28.606AA2A Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf14.hostedemail.com (Postfix) with ESMTP id D1F5060022DA for ; Mon, 2 Aug 2021 06:58:00 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id BABD121FC1; Mon, 2 Aug 2021 06:57:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1627887479; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=tUbU3ZzRUqhVzk9x8OM8/LVLgiQh8b75TwEVEjI/pNU=; b=u9FnFt7I8zkmPHO6z9sNU8KK593faYfo5bs0tUNTJh16t19zT5bFXpimOXs3mueplDYVkw U5DyEemPVD3nA7/YaiJ3vdjc55ZZGbcA9LKNxBcuqOrkay0Qi9XsACNWIL8O3wU9HKL1UU RrRiqtqE9aWaxXTMGbj3wpsJj4eW0SM= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 8E9FEA3BB2; Mon, 2 Aug 2021 06:57:59 +0000 (UTC) Date: Mon, 2 Aug 2021 08:57:56 +0200 From: Michal Hocko To: Shakeel Butt Cc: Johannes Weiner , Roman Gushchin , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] memcg: cleanup racy sum avoidance code Message-ID: References: <20210728012243.3369123-1-shakeelb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210728012243.3369123-1-shakeelb@google.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D1F5060022DA Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=u9FnFt7I; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf14.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Stat-Signature: s8usbtco4ukk5yxiwa9t43re15r1k46t X-HE-Tag: 1627887480-579847 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 27-07-21 18:22:43, Shakeel Butt wrote: > We used to have per-cpu memcg and lruvec stats and the readers have to > traverse and sum the stats from each cpu. This summing was racy and may > expose transient negative values. So, an explicit check was added to > avoid such scenarios. Now these stats are moved to rstat infrastructure > and are no more per-cpu, so we can remove the fixup for transient > negative values. > > Signed-off-by: Shakeel Butt Acked-by: Michal Hocko > --- > include/linux/memcontrol.h | 15 ++------------- > 1 file changed, 2 insertions(+), 13 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 7028d8e4a3d7..5f2a39a43d47 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -991,30 +991,19 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg, > > static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx) > { > - long x = READ_ONCE(memcg->vmstats.state[idx]); > -#ifdef CONFIG_SMP > - if (x < 0) > - x = 0; > -#endif > - return x; > + return READ_ONCE(memcg->vmstats.state[idx]); > } > > static inline unsigned long lruvec_page_state(struct lruvec *lruvec, > enum node_stat_item idx) > { > struct mem_cgroup_per_node *pn; > - long x; > > if (mem_cgroup_disabled()) > return node_page_state(lruvec_pgdat(lruvec), idx); > > pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); > - x = READ_ONCE(pn->lruvec_stats.state[idx]); > -#ifdef CONFIG_SMP > - if (x < 0) > - x = 0; > -#endif > - return x; > + return READ_ONCE(pn->lruvec_stats.state[idx]); > } > > static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec, > -- > 2.32.0.432.gabb21c7263-goog -- Michal Hocko SUSE Labs