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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 C658FC43467 for ; Thu, 8 Oct 2020 09:53:05 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E2ADD2083B for ; Thu, 8 Oct 2020 09:53:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E2ADD2083B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4C6RMy0KqBzDqT1 for ; Thu, 8 Oct 2020 20:53:02 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4C6RJ76nCPzDqRY for ; Thu, 8 Oct 2020 20:49:37 +1100 (AEDT) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4C6RHv6vbCz9v0Jb; Thu, 8 Oct 2020 11:49:31 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id mnZbLhC9ScyS; Thu, 8 Oct 2020 11:49:31 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4C6RHv5nYlz9v0JY; Thu, 8 Oct 2020 11:49:31 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id A96338B832; Thu, 8 Oct 2020 11:49:32 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id xNCjMtQPDKXQ; Thu, 8 Oct 2020 11:49:32 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id A45508B82F; Thu, 8 Oct 2020 11:49:29 +0200 (CEST) From: Christophe Leroy Subject: mm: Question about the use of 'accessed' flags and pte_young() helper To: linux-mm , "linux-kernel@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "Aneesh Kumar K.V" , Nicholas Piggin Message-ID: <31ef1305-1fd4-8159-a2ca-e9968a568ff0@csgroup.eu> Date: Thu, 8 Oct 2020 11:49:23 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" In a 10 years old commit (https://github.com/linuxppc/linux/commit/d069cb4373fe0d451357c4d3769623a7564dfa9f), powerpc 8xx has made the handling of PTE accessed bit conditional to CONFIG_SWAP. Since then, this has been extended to some other powerpc variants. That commit means that when CONFIG_SWAP is not selected, the accessed bit is not set by SW TLB miss handlers, leading to pte_young() returning garbage, or should I say possibly returning false allthough a page has been accessed since its access flag was reset. Looking at various mm/ places, pte_young() is used independent of CONFIG_SWAP Is it still valid the not manage accessed flags when CONFIG_SWAP is not selected ? If yes, should pte_young() always return true in that case ? While we are at it, I'm wondering whether powerpc should redefine arch_faults_on_old_pte() On some variants of powerpc, accessed flag is managed by HW. On others, it is managed by SW TLB miss handlers via page fault handling. Thanks Christophe