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=-3.8 required=3.0 tests=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 A759BC43441 for ; Fri, 12 Oct 2018 08:02:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7920A21470 for ; Fri, 12 Oct 2018 08:02:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7920A21470 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.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 S1727748AbeJLPd6 (ORCPT ); Fri, 12 Oct 2018 11:33:58 -0400 Received: from foss.arm.com ([217.140.101.70]:47580 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727378AbeJLPd6 (ORCPT ); Fri, 12 Oct 2018 11:33:58 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1B80FF; Fri, 12 Oct 2018 01:02:44 -0700 (PDT) Received: from [10.162.0.72] (unknown [10.162.0.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C728E3F5B7; Fri, 12 Oct 2018 01:02:41 -0700 (PDT) Subject: Re: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry To: 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> From: Anshuman Khandual Message-ID: Date: Fri, 12 Oct 2018 13:32:39 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181009131803.GH6248@arm.com> Content-Type: text/plain; charset=utf-8 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 10/09/2018 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.