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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 D435CC433E0 for ; Sat, 13 Mar 2021 15:10:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 192B464ED9 for ; Sat, 13 Mar 2021 15:09:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 192B464ED9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8F7446B0073; Sat, 13 Mar 2021 10:09:58 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8CE126B0074; Sat, 13 Mar 2021 10:09:58 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 796286B0075; Sat, 13 Mar 2021 10:09:58 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0238.hostedemail.com [216.40.44.238]) by kanga.kvack.org (Postfix) with ESMTP id 5F7466B0073 for ; Sat, 13 Mar 2021 10:09:58 -0500 (EST) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 1D17E99B4 for ; Sat, 13 Mar 2021 15:09:58 +0000 (UTC) X-FDA: 77915186076.27.8A439A0 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf25.hostedemail.com (Postfix) with ESMTP id 1C31060BF79D for ; Sat, 13 Mar 2021 15:09:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=2c246of4H/FX570UuJ3LPDfwjAVtlnkICmfbQ/jdFGo=; b=r2hnSlFRjuxycEmqtRHxY85ZYZ fjIOXexcUZr1OI1Mj1JA5mHfqrjYePWZ6zX8UNDI26IE1ev+A+VpsyOQtLpdS7IS4GtopGtT11BOG Zqr0MMiSHHrb4kqjKuEVGHKBoxOFtM3eQPuu4Nf/H/nN2YB4Sc+IZwSkduY6BrqyG1uKh+7cYbs8n UvYWHm6ubpjnw36Nxq+KwwXfsDL8S4Oq1NmalTpr3jMTUTC2eVHpYjinhiy/g9h7jjP5pWMVZgJp1 j2Zd2xHBuTOdITb9nP3u/lrl0RvinTemdZXtIOflVIzSFAOKQdX2u9u1ao0MD7c8sgTxKTrop8/C5 9/qo0RYQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lL5tG-00E8iX-BJ; Sat, 13 Mar 2021 15:09:27 +0000 Date: Sat, 13 Mar 2021 15:09:18 +0000 From: Matthew Wilcox To: Yu Zhao Cc: linux-mm@kvack.org, Alex Shi , Andrew Morton , Dave Hansen , Hillf Danton , Johannes Weiner , Joonsoo Kim , Mel Gorman , Michal Hocko , Roman Gushchin , Vlastimil Babka , Wei Yang , Yang Shi , Ying Huang , linux-kernel@vger.kernel.org, page-reclaim@google.com Subject: Re: [PATCH v1 01/14] include/linux/memcontrol.h: do not warn in page_memcg_rcu() if !CONFIG_MEMCG Message-ID: <20210313150918.GH2577561@casper.infradead.org> References: <20210313075747.3781593-1-yuzhao@google.com> <20210313075747.3781593-2-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210313075747.3781593-2-yuzhao@google.com> X-Stat-Signature: 1u7n1xxqgh5qdmo7hrzqup7c3m65kasi X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1C31060BF79D Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf25; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615648191-113019 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 Sat, Mar 13, 2021 at 12:57:34AM -0700, Yu Zhao wrote: > We want to make sure the rcu lock is held while using > page_memcg_rcu(). But having a WARN_ON_ONCE() in page_memcg_rcu() when > !CONFIG_MEMCG is superfluous because of the following legit use case: > > memcg = lock_page_memcg(page1) > (rcu_read_lock() if CONFIG_MEMCG=y) > > do something to page1 > > if (page_memcg_rcu(page2) == memcg) > do something to page2 too as it cannot be migrated away from the > memcg either. > > unlock_page_memcg(page1) > (rcu_read_unlock() if CONFIG_MEMCG=y) > > This patch removes the WARN_ON_ONCE() from page_memcg_rcu() for the > !CONFIG_MEMCG case. I think this is wrong. Usually we try to have the same locking environment no matter what the CONFIG options are, like with kmap_atomic(). I think lock_page_memcg() should disable RCU even if CONFIG_MEMCG=n.