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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no 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 02BB3C432BE for ; Wed, 28 Jul 2021 20:37:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6748360F9B for ; Wed, 28 Jul 2021 20:37:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6748360F9B Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 024B16B0036; Wed, 28 Jul 2021 16:37:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F17278D0001; Wed, 28 Jul 2021 16:37:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E05416B006C; Wed, 28 Jul 2021 16:37:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0118.hostedemail.com [216.40.44.118]) by kanga.kvack.org (Postfix) with ESMTP id C3D1A6B0036 for ; Wed, 28 Jul 2021 16:37:45 -0400 (EDT) Received: from smtpin38.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 6D798252CF for ; Wed, 28 Jul 2021 20:37:45 +0000 (UTC) X-FDA: 78413157690.38.70F7B74 Received: from mail-yb1-f176.google.com (mail-yb1-f176.google.com [209.85.219.176]) by imf21.hostedemail.com (Postfix) with ESMTP id DE94BD01B0E7 for ; Wed, 28 Jul 2021 20:37:44 +0000 (UTC) Received: by mail-yb1-f176.google.com with SMTP id q15so6158134ybu.2 for ; Wed, 28 Jul 2021 13:37:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Wx12YfrHsQsDKjajWfKvfKfUSFEaj6kJhNDgZWYmtmg=; b=QfaWHqJDwQHVJXicJ8h1hGeUi7F2r6xmPRzW3TM7SqTNre4aIPa6Oid+LKkUmQuoYa hTKe1i6Kl4llnheG7hQwB5FKG8Z7iuRdOHJSP1lv0JuVE48SfIWX3TrQ7CZB+qcY9euO 0Am/d96xgQ5QGG5MqmHO0Ggigrsc8Jo4v1cbMYjQukQBEKrfoUFuOlqIKBcsZyy0jtHu V7C1SQlrm9QF0LsyHsUfSmw33Y0SFtDdetgdYK3NirXjWa4fugAUfJd1Ook09gFLezlr gEu8tGenY41P0LTNDUqaLyGdDpTmNV7ztpPkIPovOboJAotIRxcoKsf7Bc9CVfXL6RA1 5LCA== 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=Wx12YfrHsQsDKjajWfKvfKfUSFEaj6kJhNDgZWYmtmg=; b=qzgZVYjmTeGfTM0pfimpl2gMOWJjACKqHSZYLKX54s5cZO1qY7vCObyHM5HB36EJud rOF31jFyshTDOVgOMznWgNvB/nkBr4b5Oikyt3DTHPho4wHt7wRjztmcPmPSLrjhYjuQ qUASAFlcpYtdUeRkv2cu7i+sgfsKO3FS+HfKMEXwZHsHCEBYtPbY0mF1bJEqVQc69aQ+ pu1RYSfG3KtfiVqjPbCWgfIfX5x/7k3U+NAWmHIgvUik12q79Po75GQr3IkBZ5yXbNWi tnqYJd1BJw4sXhMIeNBJNKcZU1Yy6WjvmAqdJn+iJ0jc7tRjM/lPF8KGE0K4mMTo3Qtf nvJA== X-Gm-Message-State: AOAM533hgsEwyapXSxoQUGAknGcygwXx639446enuN30o1mrTeUjjcq2 XH24t0yDb7Y8qnXFa1anT94AsS2f9oHl5RDeHhuijQ== X-Google-Smtp-Source: ABdhPJy/v9JTpm3aTY0ZFIyJlt6f/3MhsxjB6GwADapmOn411nOwrQOwiJdQvAhg3g7WjlscqM0DE/54cZRlaQua4f4= X-Received: by 2002:a25:8746:: with SMTP id e6mr2067674ybn.76.1627504663934; Wed, 28 Jul 2021 13:37:43 -0700 (PDT) MIME-Version: 1.0 References: <20210728012243.3369123-1-shakeelb@google.com> <20210728124326.a3e6cc29f670062185fb57d7@linux-foundation.org> In-Reply-To: <20210728124326.a3e6cc29f670062185fb57d7@linux-foundation.org> From: Shakeel Butt Date: Wed, 28 Jul 2021 13:37:28 -0700 Message-ID: Subject: Re: [PATCH] memcg: cleanup racy sum avoidance code To: Andrew Morton Cc: Michal Hocko , Johannes Weiner , Roman Gushchin , Cgroups , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=QfaWHqJD; spf=pass (imf21.hostedemail.com: domain of shakeelb@google.com designates 209.85.219.176 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam02 X-Stat-Signature: er55bdhshg6fyzachus5kh5r7zdhimps X-Rspamd-Queue-Id: DE94BD01B0E7 X-HE-Tag: 1627504664-11934 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 Wed, Jul 28, 2021 at 12:43 PM Andrew Morton wrote: > > On Tue, 27 Jul 2021 18:22:43 -0700 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. > > We can't do anything about the same code in lruvec_page_state_local()? lruvec_page_state_local() is used by cgroup v1's memory.numa_stat for cgroup local stats (not hierarchical) and are still per-cpu. To make it non-per-cpu, we have to add 'long state_local[NR_VM_NODE_STAT_ITEMS]' in 'struct lruvec_stats' and do aggregation in rstat flushing. So, paying the cpu traversal cost with more memory usage. I am not sure if it is worth it.