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 01273C5AD49 for ; Tue, 3 Jun 2025 17:19:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 31CE66B04C5; Tue, 3 Jun 2025 13:19:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2F4366B04C6; Tue, 3 Jun 2025 13:19:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 195C66B04C7; Tue, 3 Jun 2025 13:19:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id EBBCC6B04C5 for ; Tue, 3 Jun 2025 13:19:20 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id A1FF614113B for ; Tue, 3 Jun 2025 17:19:20 +0000 (UTC) X-FDA: 83514750480.23.474C18F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf27.hostedemail.com (Postfix) with ESMTP id 4B33D40006 for ; Tue, 3 Jun 2025 17:19:18 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=KjGHMwv2; spf=pass (imf27.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=1748971158; 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=qUU4OFf74ZE0Vbi2j5eSNHQKfn59GptFs3ll0pDTE+4=; b=AGJ3rVq17o87ZCC/Y+/PlwoqmhOPKOJwrU9CkS2alzc4oBifvYh9FdO7F4bpy+gTDYq3EY ayHyo7YneIyhh9ljw5J4z/A/pXHkg2q169FEwVyn1ngBnkcZRB26O/P1bAHX8sJccRX7QV CvNo1vf1k4OxVdbSUywJyrlLB8DAWi0= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=KjGHMwv2; spf=pass (imf27.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-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1748971158; a=rsa-sha256; cv=none; b=RE7RVx9ZVJzZ6QoB+74GOrrxbF+rvFk+rRsTsNBU9O5axC3JyCn0QztSrwgQeglXG7dB+s yUSF9Y8o3JbFoPRhRLOOgrePnOCRgl3fVPCt0lRaQIcY/c6re1j3QCOKQj6kfkVer2Artk bIbROEMLw9yllPg59y7ldTfnbsNBU9k= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1748971157; 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=qUU4OFf74ZE0Vbi2j5eSNHQKfn59GptFs3ll0pDTE+4=; b=KjGHMwv23jG41HIFWvo5hEPdrCJ5sgZtX4suOgN/s7lmP4BuzHnBWLwjIIRasa2l8fElMa 6ccL28VCm92wKJ/aVF5Ae9xGYTMOrTemOl6+cOSHW8PdhpAItB2W3d6hre7WgxTD5jpjBn aUIg6hu3kd20JlCPd7/ImaIplcQxBNc= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-101-fLCWswYYNJGGXFSdYcs20g-1; Tue, 03 Jun 2025 13:19:16 -0400 X-MC-Unique: fLCWswYYNJGGXFSdYcs20g-1 X-Mimecast-MFC-AGG-ID: fLCWswYYNJGGXFSdYcs20g_1748971155 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-450787c8626so34055245e9.1 for ; Tue, 03 Jun 2025 10:19:16 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1748971155; x=1749575955; 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=qUU4OFf74ZE0Vbi2j5eSNHQKfn59GptFs3ll0pDTE+4=; b=ABx4PQ+w/x2357c1P0RXhzFn2JJevOhAevP0G620VdfirVp2FvWaZSfYqBTPjooaDI 7Q+zZ+1uIoHTcJEzs+qdrzvvwcY6aJlC2jyUqqBFz89+9CbqBoTVErYGFDoiZ/hUl2pj qIn0sQCSRVKXkw05Hs6f9RlW2ZCkMiprREOUCK3V3z9jzpIKUTIWW8NvYpto/SC8+lnl kstZapMn5YMr6eDFHFxZmb8ziSOo10UdmvcXGywBVpP5ADxj4atTgB9ju/lhBfN6qI9G aSoxaWs6xp6FHiARzAw9Jc5zK9YNgD1rcbppBGRxIimpLbqGO1rAUVwWytQxXSAIqnIj kQjA== X-Forwarded-Encrypted: i=1; AJvYcCUp713B20wg+Wv2L49mRsVC5LJcyvTYOdwvlSxNyK+Y1FJeiXXerQuJP6qqQkZdP3393YEErFuiAQ==@kvack.org X-Gm-Message-State: AOJu0YwL5Q0qjl0AXPXZN/lokkdgZdCZZy5+nWdfODwfWaDxwCyeXT7f eS7StmGhn8TETGBZ9qytEVhoBD0RZiTzNJ9zJDRgHojP9bp8QLoiZ2y3UaFhZLvcmuuXbJvBsCx E2BgYHfHw/5DqDo0MrrHczG13zI4XQq3ImgS2iBNirhmWKpNS4smH X-Gm-Gg: ASbGncvXspQic9lp1xltbbx6l7N4hNpBypOTRsTfC17wbjmh0kfGs38wowAClFRstqQ 8g3w6EuBIeerlPShrxCK2ejV/u95+IyY/sCOIIEnYVWe0EzOyaIGNa5fBorm9TE9kAzNqHIhzIH czsk1Qgok+aY2w4BpDLGKf9mgCCBfdRV1P1/Rx4vGf7nqSh9+WJRdbveVyY+4kQexJH1ojf+SPz 3sJwaWI35l+ITm+u0iYNRUIyplhpm1WVtwrGAV+RYopIdW8qbT83dN5UDkm0y/+JL4phphbZJFz 2nxh4NCcrs9QzWLtooLQV6vcAwK0rmVHRUZiFYTYQzMezvxXHuPB2xFbbmPqcyvUght3tKhZuFA 17x/0jY8n7Xf+Ab91kVJ97kWyoBfG5+meSvrwNwU= X-Received: by 2002:a05:600c:3596:b0:43d:160:cd97 with SMTP id 5b1f17b1804b1-4511edf2167mr105293365e9.25.1748971155355; Tue, 03 Jun 2025 10:19:15 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFj7GIZlVjMRe5WGKxNpZPxEoYl4Ep47THdwCv36w36DKQBMvC50/+cJNUD1tUkHQAZp+l14w== X-Received: by 2002:a05:600c:3596:b0:43d:160:cd97 with SMTP id 5b1f17b1804b1-4511edf2167mr105293095e9.25.1748971154970; Tue, 03 Jun 2025 10:19:14 -0700 (PDT) Received: from ?IPV6:2003:d8:2f0d:f000:eec9:2b8d:4913:f32a? (p200300d82f0df000eec92b8d4913f32a.dip0.t-ipconnect.de. [2003:d8:2f0d:f000:eec9:2b8d:4913:f32a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-451e505c350sm29892395e9.0.2025.06.03.10.19.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Jun 2025 10:19:14 -0700 (PDT) Message-ID: <1602a87b-b1bc-4b53-abe7-dce8adddbe46@redhat.com> Date: Tue, 3 Jun 2025 19:19:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/3] mm, hugetlb: Clean up locking in hugetlb_fault and hugetlb_wp To: Peter Xu Cc: Oscar Salvador , Andrew Morton , Muchun Song , James Houghton , Gavin Guo , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250602141610.173698-1-osalvador@suse.de> <20250602141610.173698-2-osalvador@suse.de> 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: 74JY9TwjoGmJzsXjf5zLyj9IETtO7neesJLx4VAdxjA_1748971155 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-Stat-Signature: b9ai83qkdcrkoc8jgoiaie6wmjge4fpk X-Rspamd-Queue-Id: 4B33D40006 X-Rspamd-Server: rspam11 X-HE-Tag: 1748971158-989500 X-HE-Meta: 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 sDS3QmIJ Nh8y7N0PvBI4NKmbM/4eeK+Wg+9IiJkvuVS3ew63VD7rytB7Vq7PkPaxKeclAdG4ZPe/mioF0RHOMgP5td53dF+1NWUsGUQ7WjNXf2vBxkxqSBt4oAvREoyI1GA== 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: >> As stated elsewhere, the mapcount check + folio_move_anon_rmap need the >> folio lock. > > Could you elaborate what would go wrong if we do folio_move_anon_rmap() > without folio lock here? Just to make sure we're on the same page: we > already have pgtable lock held, and we decided to reuse an anonymous > hugetlb page. For now we have VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); right at the beginning of folio_move_anon_rmap(). That dates back to commit c44b674323f4a2480dbeb65d4b487fa5f06f49e0 Author: Rik van Riel Date: Fri Mar 5 13:42:09 2010 -0800 rmap: move exclusively owned pages to own anon_vma in do_wp_page() When the parent process breaks the COW on a page, both the original which is mapped at child and the new page which is mapped parent end up in that same anon_vma. Generally this won't be a problem, but for some workloads it could preserve the O(N) rmap scanning complexity. A simple fix is to ensure that, when a page which is mapped child gets reused in do_wp_page, because we already are the exclusive owner, the page gets moved to our own exclusive child's anon_vma. My recollection is that the folio lock protects folio->mapping. So relevant rmap walks that hold the folio lock can assume that folio->mapping and thereby folio_anon_vma() cannot change. folio_lock_anon_vma_read() documents something regarding the folio lock protecting the anon_vma. I can only speculate that locking the folio is cheaper than locking the relevant anon_vma, and that rmap code depends on that. I'll note that in the introducing commit we didn't use the WRITE_ONCE, though. That was added in commit 16f5e707d6f6f7644ff07e583b8f18c3dcc5499f Author: Alex Shi Date: Tue Dec 15 12:33:42 2020 -0800 mm/rmap: stop store reordering issue on page->mapping But I don't think that the folio lock was a replacement to that WRITE_ONCE. -- Cheers, David / dhildenb