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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 E009EC433B4 for ; Sat, 10 Apr 2021 17:47:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 69281611C9 for ; Sat, 10 Apr 2021 17:47:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 69281611C9 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B7B078E0002; Sat, 10 Apr 2021 13:47:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B529A8E0001; Sat, 10 Apr 2021 13:47:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A1A4A8E0002; Sat, 10 Apr 2021 13:47:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0248.hostedemail.com [216.40.44.248]) by kanga.kvack.org (Postfix) with ESMTP id 86B8E8E0001 for ; Sat, 10 Apr 2021 13:47:23 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 339C94DA2 for ; Sat, 10 Apr 2021 17:47:23 +0000 (UTC) X-FDA: 78017189166.20.3ABBFA1 Received: from mail-lf1-f41.google.com (mail-lf1-f41.google.com [209.85.167.41]) by imf19.hostedemail.com (Postfix) with ESMTP id 4E30B90009F2 for ; Sat, 10 Apr 2021 17:47:11 +0000 (UTC) Received: by mail-lf1-f41.google.com with SMTP id b4so14708911lfi.6 for ; Sat, 10 Apr 2021 10:47:22 -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=YgtCeA1Y4wCp3r4IZqk+RljjksiftqBoFrg1EOiiX98=; b=LpEUse8MvSsBjR/LUs2dYtDHrydq5lyD4O4gsodi1yEPM1SHXLqHM0JxMtitWaQN9H EjVClxjmcjV/R3akgoMCcpKdQjKgXDny3p99W67WidjZKzmra53wR4VT60QnK8HQT7Hy KObIDGfQuKYiK1rQUpzwWidXgMky7nMhfZX9nHu6GsS+z9cbbFKMC668EiZU2TKXuBnW RfcXHqLce4uv0mbDhLIJT8IYwd775JtTIMO6SeuVcDDtLfC89Dm67GRetRPt4ju4w0EF SjMbS/9O6WMx3RjMRPCEDRyXXXviVegPcT2E+QzPNL4qy1wqzPD2ylChZxW2hPoRbF+p akVg== 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=YgtCeA1Y4wCp3r4IZqk+RljjksiftqBoFrg1EOiiX98=; b=JmEKg6JbtiK0k+uPHn6V0s2P3Its1F5sDbOt6mLa6SQVKE2XAeoFfwKWZX/7SToLod hin7jG5vjhOSi00Zu0ljQnPAdcdbKTl+NrCY+z4egZfk/8SODxYrYtsughlHWnna7L5z ASuUklcUWHGPZaLQoPZl8j7qFCWF6+IxclPDMR0kZcFNlD2Ul0o5kiwtrTJJ+JkvDCQZ 3cYAzkR2xznHbKYx/JO6tBmXkiOk/Waw32V7Cg/TzeZ9nVJJfFTThvBts64CA1PjMJly 78wtaSMFiyPhnlVUi5y5cSh7Xc3aw8pq8I4KRKafwCVbSbJnw5w8nEqKXc69g4ZS4xyW gtNg== X-Gm-Message-State: AOAM530W8UeSuiqF1Mpku3XjwfJW8FcwesMpTeoyP5TO+dgzOhzgn86h jlXYBsbXDZs2ibeCzOju02QnpBiSrZbKaJQei5uqvQ== X-Google-Smtp-Source: ABdhPJyrJ9OtawfTPWSGdv8LD+6QkmBdDM6JV5MAKUk0DwXB9KTifdsnQzGpekz9zSTIOufp5RVbxrgLQ95h3NYYcXs= X-Received: by 2002:a05:6512:2019:: with SMTP id a25mr4230772lfb.347.1618076841358; Sat, 10 Apr 2021 10:47:21 -0700 (PDT) MIME-Version: 1.0 References: <20210409122959.82264-1-songmuchun@bytedance.com> <20210409122959.82264-3-songmuchun@bytedance.com> In-Reply-To: <20210409122959.82264-3-songmuchun@bytedance.com> From: Shakeel Butt Date: Sat, 10 Apr 2021 10:47:08 -0700 Message-ID: Subject: Re: [RFC PATCH v2 02/18] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm To: Muchun Song Cc: Roman Gushchin , Johannes Weiner , Michal Hocko , Andrew Morton , Vladimir Davydov , LKML , Linux MM , Xiongchun duan , fam.zheng@bytedance.com, Balbir Singh , Yang Shi , Alex Shi , Dan Schatzberg Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4E30B90009F2 X-Stat-Signature: e4wdxukstbbpectwfqqozkrtdzit3a3g Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf19; identity=mailfrom; envelope-from=""; helo=mail-lf1-f41.google.com; client-ip=209.85.167.41 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618076831-536215 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 Fri, Apr 9, 2021 at 5:32 AM Muchun Song wrote: > > When mm is NULL, we do not need to hold rcu lock and call css_tryget for > the root memcg. And we also do not need to check !mm in every loop of > while. So bail out early when !mm. > > Signed-off-by: Muchun Song > Acked-by: Johannes Weiner Reviewed-by: Shakeel Butt