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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 C750BC28CF8 for ; Mon, 15 Oct 2018 08:32:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6789D20853 for ; Mon, 15 Oct 2018 08:32:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="V75fnljr" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6789D20853 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726794AbeJOQRM (ORCPT ); Mon, 15 Oct 2018 12:17:12 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:43461 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726583AbeJOQRM (ORCPT ); Mon, 15 Oct 2018 12:17:12 -0400 Received: by mail-pf1-f194.google.com with SMTP id p24-v6so9294174pff.10 for ; Mon, 15 Oct 2018 01:32:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:subject:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=yq4s+teHWk6mhEQ7xflzL98C7IKgJ0BsTWv7BiVEvw4=; b=V75fnljrk2PIihZEaj2DTWFuACO7MgdwwqsElB24EYsV9nprzptEKY7l6x/V5IAZbZ JJE3hlOnOOJUCaGAjjzC07CwkgcRjRFO6lROKiflSRvHZiDXN054KIvagTGubLUIJP2Z lan5A62x4hYvjK8rxZQZAc6Fasea3jWZKY2KcyBDe+cm20TKjiyvTA4xLcIEA4L+lu7n E7dzgiYQQmLW5eupQWHDgszafP6m2QZO7q9lyAbYL/HFvd64GWsKHKYjb5WnmvpBfdkE H3EgG2clIWYJxb1+Ka/WeeaUCAJBKuYu4MIJk2zJPnszZbQdso+KSmb0ojIHk4elE4Mq bMSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=yq4s+teHWk6mhEQ7xflzL98C7IKgJ0BsTWv7BiVEvw4=; b=pM6R9QY535Dwqa5tqQtnxJ/bUwg4I4rHtXbox81dLDnRftCkFmph+MMuP4DtQ6c7Az 38uqvBseg7s6D1DBOxVGsufXuNGn3HhZQTlec83S0pMvdRPYEABcjaqSB0Bsya2w/pNU kdb8K4elVH3EvGtRlNUPM2tIyUwRbVaYFnG/TG0PgjquyHbyYSU/uL7t6OEYaDCxaGF4 bsk7N+zz2j/gyb7HSu1YyLYkogO6ipm3/kYbLCTVjcXl+pyWInH3fvKZXTpBoGEDa72s g10IuC6DA8dG3eXKQHLvdZj40Tu6KvemkK4Em4gQXJa8hDF5oi2PcEZRBDWxSFtqSsqf wi2Q== X-Gm-Message-State: ABuFfoiMAH2GGokHtZcOT6p+EUMGcSF+PVXJCdC2zo+OijLuLNOBkVCc t+rkBTLIVU7UaifV5n+FUQk= X-Google-Smtp-Source: ACcGV60TWM7AB0FTbAoytATzjAWd3wn5X7LCbi275/s/k/nFmiUkffHvckOZ/TwHl30wQuINeip5ug== X-Received: by 2002:a62:67c3:: with SMTP id t64-v6mr9097463pfj.76.1539592373718; Mon, 15 Oct 2018 01:32:53 -0700 (PDT) Received: from [192.168.0.123] ([49.207.50.246]) by smtp.gmail.com with ESMTPSA id v26-v6sm5904810pfg.43.2018.10.15.01.32.49 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Oct 2018 01:32:52 -0700 (PDT) From: "Aneesh Kumar K.V" X-Google-Original-From: "Aneesh Kumar K.V" Subject: Re: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry To: Anshuman Khandual , Will Deacon , "Kirill A. Shutemov" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, akpm@linux-foundation.org, mhocko@suse.com, zi.yan@cs.rutgers.edu References: <1539057538-27446-1-git-send-email-anshuman.khandual@arm.com> <20181009130421.bmus632ocurn275u@kshutemo-mobl1> <20181009131803.GH6248@arm.com> Message-ID: <4bf3951d-410f-fac4-dfb2-7dee5568e6ff@linux.ibm.com> Date: Mon, 15 Oct 2018 14:02:48 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12/18 1:32 PM, Anshuman Khandual wrote: > > > On 10/09/2018 06:48 PM, Will Deacon wrote: >> On Tue, Oct 09, 2018 at 04:04:21PM +0300, Kirill A. Shutemov wrote: >>> On Tue, Oct 09, 2018 at 09:28:58AM +0530, Anshuman Khandual wrote: >>>> A normal mapped THP page at PMD level should be correctly differentiated >>>> from a PMD migration entry while walking the page table. A mapped THP would >>>> additionally check positive for pmd_present() along with pmd_trans_huge() >>>> as compared to a PMD migration entry. This just adds a new conditional test >>>> differentiating the two while walking the page table. >>>> >>>> Fixes: 616b8371539a6 ("mm: thp: enable thp migration in generic path") >>>> Signed-off-by: Anshuman Khandual >>>> --- >>>> On X86, pmd_trans_huge() and is_pmd_migration_entry() are always mutually >>>> exclusive which makes the current conditional block work for both mapped >>>> and migration entries. This is not same with arm64 where pmd_trans_huge() >>>> returns positive for both mapped and migration entries. Could some one >>>> please explain why pmd_trans_huge() has to return false for migration >>>> entries which just install swap bits and its still a PMD ? >>> >>> I guess it's just a design choice. Any reason why arm64 cannot do the >>> same? >> >> Anshuman, would it work to: >> >> #define pmd_trans_huge(pmd) (pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT)) > yeah this works but some how does not seem like the right thing to do > but can be the very last option. > There can be other code paths that makes that assumption. I ended up doing the below for pmd_trans_huge on ppc64. /* * Only returns true for a THP. False for pmd migration entry. * We also need to return true when we come across a pte that * in between a thp split. While splitting THP, we mark the pmd * invalid (pmdp_invalidate()) before we set it with pte page * address. A pmd_trans_huge() check against a pmd entry during that time * should return true. * We should not call this on a hugetlb entry. We should check for HugeTLB * entry using vma->vm_flags * The page table walk rule is explained in Documentation/vm/transhuge.rst */ static inline int pmd_trans_huge(pmd_t pmd) { if (!pmd_present(pmd)) return false; if (radix_enabled()) return radix__pmd_trans_huge(pmd); return hash__pmd_trans_huge(pmd); } -aneesh