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=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 A358CC433E0 for ; Wed, 10 Mar 2021 21:45:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 662DA64FC9 for ; Wed, 10 Mar 2021 21:45:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232128AbhCJVo5 (ORCPT ); Wed, 10 Mar 2021 16:44:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232133AbhCJVob (ORCPT ); Wed, 10 Mar 2021 16:44:31 -0500 Received: from mail-pg1-x531.google.com (mail-pg1-x531.google.com [IPv6:2607:f8b0:4864:20::531]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2FFB1C061574 for ; Wed, 10 Mar 2021 13:44:31 -0800 (PST) Received: by mail-pg1-x531.google.com with SMTP id t37so1478660pga.11 for ; Wed, 10 Mar 2021 13:44:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=F1rP/HK0MUpthdudkFLSzT5JtnfPSdIqufAWiqCyWfE=; b=WX3V1AKQraPws2f/CLbZSrzfKO5shyl+APrsP1fTvCPUV8TNkxbdFcWlcAXvozZLXd kifrWLi/f8JJdtI0PL736rcBkXvmm/jZFTlNH0MSk9iLJJctqmFyrpZyTY1od6ejsP8+ 4NIRB5hL3/0+8sjcNd9CFCZxm8V27X9MNja1bxX4w3I1Ksg+rQyNJ4pHHlcDhezxYAAA tv/WRm1pKgKAUPMd7ejAS2p1IwZYAuq+xW8mlQNpCDbeCSDLkGlO0Ik1NsWecDZTHeTL QLqSm+ZhNHi4cgc+rsAI+3aVXSClw6g1/mumkg10Ago+jQISGbxzKc1ba8nHk6Juoivh m4uQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=F1rP/HK0MUpthdudkFLSzT5JtnfPSdIqufAWiqCyWfE=; b=SrwEvCfizRNaCismVPlf8EtDx62wBnxLBLkonV4+p+qylCBhpS8b8JJhMvZlF2vFm1 BmZKGrQCUe+5fzZS0HIBY/40k4yHZIgU+e0FIf4Kh/m1YqbVpAReQaDzutqRc8hlb0h4 XyiWQReZXfplPl3e1JcGwqpbvV/EMG+nb2CIlB5/g/VEO8AESGsk+6pAXWCo7KXPe1tl SBO0EQB6HjeE5yZIoqo129ATTXgr5monwoogQV5E7+Czl8XwU2Orv1yNdc4NwnzZXEpG E+zXrP7nhR7Xs9UO2PoNv125Qad5lRrZngr8uaxkHpXu4OgG1kVgN5SHh4cUujJ/FR9K Jj/Q== X-Gm-Message-State: AOAM532gSDsTg3KjmvMvZi4JvIMEVCOIowFtNZhFHGYND410lI55ABMT owvE6PWGfwYQz0NqcPUvxck= X-Google-Smtp-Source: ABdhPJypsSKXx5n5ORV+uEvNyrGd64CkLtPHIiDVVoGJhkcs5JqN2IsQm46LGimngeRfP8puqcbJcA== X-Received: by 2002:a65:6a48:: with SMTP id o8mr4411929pgu.424.1615412670705; Wed, 10 Mar 2021 13:44:30 -0800 (PST) Received: from f8ffc2228008.ant.amazon.com ([54.240.193.1]) by smtp.gmail.com with ESMTPSA id a7sm407994pfo.105.2021.03.10.13.44.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Mar 2021 13:44:29 -0800 (PST) Subject: Re: [PATCH v2 1/2] mm/memcg: rename mem_cgroup_split_huge_fixup to split_page_memcg To: Michal Hocko Cc: Zhou Guanghui , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, hannes@cmpxchg.org, hughd@google.com, kirill.shutemov@linux.intel.com, npiggin@gmail.com, ziy@nvidia.com, wangkefeng.wang@huawei.com, guohanjun@huawei.com, dingtianhong@huawei.com, chenweilong@huawei.com, rui.xiang@huawei.com References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-2-zhouguanghui1@huawei.com> <3ad50842-881f-eb88-a14d-0b6c70ce33d2@gmail.com> From: "Singh, Balbir" Message-ID: Date: Thu, 11 Mar 2021 08:44:22 +1100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/3/21 7:28 pm, Michal Hocko wrote: > On Tue 09-03-21 09:37:29, Balbir Singh wrote: >> On 4/3/21 6:40 pm, Zhou Guanghui wrote: > [...] >>> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> /* >>> - * Because page_memcg(head) is not set on compound tails, set it now. >>> + * Because page_memcg(head) is not set on tails, set it now. >>> */ >>> -void mem_cgroup_split_huge_fixup(struct page *head) >>> +void split_page_memcg(struct page *head, unsigned int nr) >>> { >> >> Do we need input validation on nr? Can nr be aribtrary or can we enforce >> >> VM_BUG_ON(!is_power_of_2(nr)); > > In practice this will be power of 2 but why should we bother to sanitze > that? > Just when DEBUG_VM is enabled to ensure the contract is valid, given that nr is now variable, we could end up with subtle bugs unless we can audit all callers. Even the power of 2 check does not catch the fact that nr is indeed what we expect, but it still checks a large range of invalid inputs. Balbir Singh.