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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A14BC71136 for ; Mon, 16 Jun 2025 09:22:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 299B46B0088; Mon, 16 Jun 2025 05:22:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 250436B0089; Mon, 16 Jun 2025 05:22:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 139826B008A; Mon, 16 Jun 2025 05:22:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 04B3A6B0088 for ; Mon, 16 Jun 2025 05:22:53 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 6BC2F80D6F for ; Mon, 16 Jun 2025 09:22:51 +0000 (UTC) X-FDA: 83560724142.17.7918135 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf01.hostedemail.com (Postfix) with ESMTP id E7C3140003 for ; Mon, 16 Jun 2025 09:22:48 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HDEQwkoz; spf=pass (imf01.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1750065769; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=UBp58qTRV+cYxQwSpwgzVisxa2vKGUXxS+M1OQFGddU=; b=xLYU9MlyNLJXCl0zF2CsmLYiXLe1hNkBReoLsOJUd5DbtlP6W1jtdaonC5h6xc9J7ySi3V bj1QwMErnKA4id30Zxuvq6MvRh2xRhKifa0rWHLumEvilYlAzLhqWjvw51I6ALEVG1mBmE ceMinQ9e+k6MNq0HJqmhEZHFyL3HCuo= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1750065769; a=rsa-sha256; cv=none; b=l49OyIk5BKmVkhfnNSdmpfCbbj5DjkYdG7qCsq39rWdr9tqFRZCCNEXNCj7guYCKIqzjnN Cyoi/nyvsuirIT1xFZ/49hE7tHISRZq+HKJomRwdmMSYpSkCVqIZLGt+yLJyTeYgAJCZXN gwyJTEHgHGV0ZxReFjVXY5ISfj1vRw8= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HDEQwkoz; spf=pass (imf01.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1750065768; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=UBp58qTRV+cYxQwSpwgzVisxa2vKGUXxS+M1OQFGddU=; b=HDEQwkozWCmRQhnwlWQn9kTUohGNjYGMOdYH3iOI7puVrtdogBt1TAMhCZx8MULO5A2DJx 53rbeeYgE9DDviyqbDFsFvGyQlbmGAhBXAb1GJ2K0Q0G23L7fZtTO+640M2fin0augDHc/ ZtTDU6lW6500pUzTNwg29y9mAmAj2l0= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-215-hM59V7NzM3CZ3z2Hgz8lzA-1; Mon, 16 Jun 2025 05:22:46 -0400 X-MC-Unique: hM59V7NzM3CZ3z2Hgz8lzA-1 X-Mimecast-MFC-AGG-ID: hM59V7NzM3CZ3z2Hgz8lzA_1750065765 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-3a52cb5684dso2466414f8f.3 for ; Mon, 16 Jun 2025 02:22:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750065765; x=1750670565; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=UBp58qTRV+cYxQwSpwgzVisxa2vKGUXxS+M1OQFGddU=; b=aNyEnnsPPgAEaA+6VpNPPoBOtUNIWVq0c2qJm1iq4URmgHFva0AdBsqc9uQufG9ndt bavroXGMiFtV0z9B3T4YJn7fRqnJBs78ILZfugJQCSeUGavhLUKtXkRIn8NFpGqd3SYO rQW102otHwo0syVAl2+J8WnFyKr9I1dCCdv1OgYMOGLBiudetnGicSxCeLSGzsaYpQqq BvXy/ad0o21SiBIANqCgq9RNTRQVn/8Gh7az6c4emvh8DZOaW2EdLnwDEDBoyiMLYPqX 5i5fGOBf1BMMfX+mDHqyABJYxThJ5o/YRrBhq7v/oGEf8dPI1nd5u0Ck/o1zFR0tYSrH RewA== X-Forwarded-Encrypted: i=1; AJvYcCXCZ0KBkw9RkclEWvpzu/AtStQN/jAeEDNV0aa0DCdg3bDioNOCxqhvrGi0+v3EsRfmc08oUapMWw==@kvack.org X-Gm-Message-State: AOJu0YxghhUm4hipHTqJTXnrK3EUYKP6JClvf7ILqG+w/8t+O8a0859f 1JlH11yBGg/OSqz1AW9gCDoG01+r6kUvJggpSInOou2gAIUwrw/BrCZiWY15o+ekxxsQLP/PkZm tyykSgeNv1DiP4j8ZOccoaO9wlvQeZRDJhOuyiqy78iNeK+lGGVYa X-Gm-Gg: ASbGncsmjrVAFDj4TcsSPHCnRz9HSuPy1cTdZwXtm59h4tiaz0H9Ha4kLSXrfW9PD2e CSJYMgilvOdJJWFVSwqbjwe3PbbxDZAwSN1WTSy1pdu2INxJBmFHEa02JtlqytS13K13cxwCzq8 N/aOTruISKv8WuRI04osNurV7vvhG8iFZD1v1Lvn/4b8sMfGjONrBnRHUkxVZkabLqnri29M3nr 7oNWCToxgXET4JZ7eraBCW13prlBM9ikz/hm55vXxtTHhrsJKHJHPBGonnhzqvcPWJPz5Y2D9/S 376UQ5IGc/2FH2AocwNHyivb8327deuwl2TQthrj3RqBuR7UhiAdHZxlsZIhA9Rg4sxQvvFd5LA C+J32mb5OUma28F/oms4lJWPS4Fw4aJZpy73y/MkCOalluKU= X-Received: by 2002:a05:6000:1888:b0:3a5:2949:6c38 with SMTP id ffacd0b85a97d-3a572e99690mr7512755f8f.52.1750065765255; Mon, 16 Jun 2025 02:22:45 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFVgWvb1lvlhTo/Z1qWtDSjFvFI6TANhcAEBmOLtt7hjJLoV4KTqnzo7eEfQlPPBx3hv/xN6Q== X-Received: by 2002:a05:6000:1888:b0:3a5:2949:6c38 with SMTP id ffacd0b85a97d-3a572e99690mr7512723f8f.52.1750065764846; Mon, 16 Jun 2025 02:22:44 -0700 (PDT) Received: from ?IPV6:2003:d8:2f25:bd00:949:b5a9:e02a:f265? (p200300d82f25bd000949b5a9e02af265.dip0.t-ipconnect.de. [2003:d8:2f25:bd00:949:b5a9:e02a:f265]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b087a9sm10713185f8f.55.2025.06.16.02.22.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jun 2025 02:22:44 -0700 (PDT) Message-ID: Date: Mon, 16 Jun 2025 11:22:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] mm,hugetlb: Document the reason to lock the folio in the faulting path To: Oscar Salvador Cc: Andrew Morton , Muchun Song , James Houghton , Peter Xu , Gavin Guo , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250612134701.377855-1-osalvador@suse.de> <20250612134701.377855-3-osalvador@suse.de> <44f0f1cc-307a-46e3-9e73-8b2061e4e938@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 7g5E32W9ys7aVAZ1iSQ7M4s2TuLwGe0AMZv4EuTaXh0_1750065765 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E7C3140003 X-Stat-Signature: nkbf5aaqki6t9adrcok3ro6bqp4n5o7y X-HE-Tag: 1750065768-152910 X-HE-Meta: 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 GXSTJXWH f7e9/w/o+jsdYaodMAWD5SP5134sDLULwDlCJXXKfujEGZWZ463rDWrjHXkGyp4QZgh88HIK5MOK7w+T+3eue53NTqdAqQLixBQNADufdYK1NeCN97Ux2yTt6IVu5mxPCs9X0r0PB6BCA0CsMncnQ9HCFwwmsb3kabkqFdCdtWfTyJIoUZPSgIu2L4i9xetw13T4TNsQvY3o9V5Uei6C4lUL9ZScT/pSq4eL8P8sYG8vVSQJ4mwLnl9SZKLwtFzxIBC5AL1fmkjNnks5qSORAIXxAezmQSNn5Dx+wWaQGOZrdzWSqk1gXimbYW+mcxPlF9ho/STpiQGR0aZ258+aK6kpKM6j6GhNhraDQ3B7wbWDmvVdCYFuRg6b/Bh1Ik1eMLsahR/yo4dKal0zkUJTGiEpmVntOpzErkNmgHXdm+0Mz4eCLsjkwM+Ln9w== 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: List-Subscribe: List-Unsubscribe: On 14.06.25 11:07, Oscar Salvador wrote: > On Fri, Jun 13, 2025 at 11:47:50PM +0200, Oscar Salvador wrote: >> Maybe it's because it's Friday, but I'm confused as to why >> do_pte_missing()->do_fault()->do_cow_fault() holds the lock while do_wp_page() doesn't >> although it might the file's page we have to copy. > > Scratch that, I see my confusion. > The first time we map the file privately, the folio must remain stable. > But if we already mapped it privately before (R/O), and we write fault on it, > we don't need to be stable (e.g: uptodated). > > But I think my comment on hugetlb_no_page() still holds, because > > hugetlb_fault->hugetlb_no_page->hugetlb_wp > > would be similar to do_pte_missing->do_cow, and in do_cow we hold both > the reference and the lock. Well, there is an important difference: hugetlb_fault->hugetlb_no_page->hugetlb_wp already *mapped* the pagecache page into the page table. See if (anon_rmap) hugetlb_add_new_anon_rmap(folio, vma, vmf->address); else hugetlb_add_file_rmap(folio); So at that point it would be "stable" unless I am missing something? So once we are in hugetlb_wp(), that path much rather corresponds to do_wp_page()->wp_page_copy. > Were we might not need the lock is in hugetlb_fault->hugetlb_wp, which > would be similar to do_wp_page()->wp_page_copy. Exactly. > Of course we will need to take it if it is an anonymous folio because we need > to check the re-use case. Yes. > > So, it gets complicated because hugetlb_no_page() needs to call > hugetlb_wp() with the lock held in case it is a pagecache folio, Per above discussion: why? After we mapped the pagecache folio, we can unlock the folio I think. and > and the same time hugetlb_wp() needs to take the lock if it us an anonymous > one for the re-use case. I think it hugetlb_wp() really only needs the lock for the anon folio. -- Cheers, David / dhildenb