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 8D48BC10F15 for ; Tue, 23 Apr 2024 10:18:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F19836B00F4; Tue, 23 Apr 2024 06:18:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EC87E6B00F5; Tue, 23 Apr 2024 06:18:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D69456B00F6; Tue, 23 Apr 2024 06:18:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id B94D86B00F4 for ; Tue, 23 Apr 2024 06:18:52 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 406D41C13CC for ; Tue, 23 Apr 2024 10:18:52 +0000 (UTC) X-FDA: 82040398104.09.F91A9C7 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf06.hostedemail.com (Postfix) with ESMTP id EB50718001C for ; Tue, 23 Apr 2024 10:18:49 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=fZ2Ot5V4; spf=pass (imf06.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1713867530; 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=HDNawudJ5KxjrW1cTaXxr2mViO8x3m4Lig3Uidmvkq8=; b=TDhDkki89ae0UjfZxz0C4+GzxtCVpzOOUmlgOxmnStX5zusPm1H0xpdhOdrRC41vYK0e9r ApXeVOJaddEi+ju77+FMswoJsslcqs2hs8lY7j890rRbzODoaHnn/I0kHmljI0GbPsa+xt FhF0mBBlbMxYgulpyXomW5C+Rhkwyvc= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1713867530; a=rsa-sha256; cv=none; b=VMTrzVi5Mq2UkfNIPQY9MrOH/qR2cAgBWrQy9rTJXUnSVJ96lL/DNMnht+gec3fDzJwYpH hIFb8z8VZLVy6iosXnYhBFNbOWXpeJ8mODkbattmfDxob66pGfGqcBG5ECU5jC7t13wQWw QLRhIBjGM6KQduF7P8p6f9JODKGvZOk= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=fZ2Ot5V4; spf=pass (imf06.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1713867529; 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=HDNawudJ5KxjrW1cTaXxr2mViO8x3m4Lig3Uidmvkq8=; b=fZ2Ot5V4KySoDHSVhjcpmCTaB3ZsNYXpnKqo9wzI2O8YFAlnQHkcfYE8ex4NWwacWgvIdg HSUDQfmSsIYl7EJexH/rOgP+4qexKDMRy+PFBNpuHTs+9qssTUlmaGKJSQ17AyqVrxiJlp bXDqMfmhhH2ZjyVcU400CYAHLr5kdz8= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-656-AELaOXRXMHWuu2cjlZxK5w-1; Tue, 23 Apr 2024 06:18:47 -0400 X-MC-Unique: AELaOXRXMHWuu2cjlZxK5w-1 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-343f5059c5fso3621172f8f.2 for ; Tue, 23 Apr 2024 03:18:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713867526; x=1714472326; 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=HDNawudJ5KxjrW1cTaXxr2mViO8x3m4Lig3Uidmvkq8=; b=jThuovikXtDIRVs3W4ZI51fUQKndl/lhVqoJAu4rlaZzaPAHcK/5ODB9BekBut6X1H cJQ+Wgec1mA8cPmgrV8flfgigo9thwUHddUUhCVhhyzuNxwxyEFdtkbHONcJZ6w0Y7iq aFl8WFVHgLZbKwgGke2ZHixOD1DLDVZ8dbwWoP1m80XW+QYCnypYH/te4ySt/S5ugstS 8DZ2NDX3+GaIvTLFTaCgrkbjdj7a2gaVWS73k9hn9JCVNXEXCIpLTA60LkfSDyG2Ml+i IkMWC6bfnohBa92s02jDTMIqKPC0fiq+I3V5wolh2IGZQnjCymI3eMbl62zEsIkiN2q9 gLTw== X-Forwarded-Encrypted: i=1; AJvYcCUWdWHK7M3jHOYN1unZNF4f9ZYLDhoezYOSCHjEnuTtUwcXjhL8sg9DswqrO4N5bRONSl2HtpJ6G2MzL+z+CWWxxPM= X-Gm-Message-State: AOJu0YyEE8LT3yy2+uwepHofStf4aN8yEWauaLA59zopk7y5eQw1Ealq jziG+YbY1k3D3+rjk7GY0ErFjwIqXaF92IA+CPZ+/UK0BjpMi2WYv5O6tcjVqcO7CkBVlHbtIDW 3q5AlAE+H9HPVZWuM5hVDh8MkzVkXblFpXc6DWjs28WOvlAQ4 X-Received: by 2002:a5d:6a8b:0:b0:349:7e8e:b29a with SMTP id s11-20020a5d6a8b000000b003497e8eb29amr9070119wru.62.1713867526584; Tue, 23 Apr 2024 03:18:46 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGPVkU2MPXUn0s5SXRSrCOpAdgk3C7A2u2zWDvzNMqHuldKbcFiFQQ3w9k9fuuzRCYAgc+Njw== X-Received: by 2002:a5d:6a8b:0:b0:349:7e8e:b29a with SMTP id s11-20020a5d6a8b000000b003497e8eb29amr9070103wru.62.1713867526143; Tue, 23 Apr 2024 03:18:46 -0700 (PDT) Received: from ?IPV6:2003:cb:c706:fd00:fb07:92f8:8f0c:6a08? (p200300cbc706fd00fb0792f88f0c6a08.dip0.t-ipconnect.de. [2003:cb:c706:fd00:fb07:92f8:8f0c:6a08]) by smtp.gmail.com with ESMTPSA id a3-20020adffb83000000b0034b32e5e9ccsm3746231wrr.64.2024.04.23.03.18.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Apr 2024 03:18:45 -0700 (PDT) Message-ID: <03cf371d-6473-463b-8586-f3ee794d8ed3@redhat.com> Date: Tue, 23 Apr 2024 12:18:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 0/4] Reduce cost of ptep_get_lockless on arm64 To: Ryan Roberts , Mark Rutland , Catalin Marinas , Will Deacon , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Andrew Morton , Muchun Song Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240215121756.2734131-1-ryan.roberts@arm.com> <86680856-2532-495b-951a-ea7b2b93872f@arm.com> <35236bbf-3d9a-40e9-84b5-e10e10295c0c@redhat.com> <4fba71aa-8a63-4a27-8eaf-92a69b2cff0d@arm.com> <5a23518b-7974-4b03-bd6e-80ecf6c39484@redhat.com> <81aa23ca-18b1-4430-9ad1-00a2c5af8fc2@arm.com> <70a36403-aefd-4311-b612-84e602465689@redhat.com> <3e50030d-2289-4470-a727-a293baa21618@redhat.com> <772de69a-27fa-4d39-a75d-54600d767ad1@arm.com> <969dc6c3-2764-4a35-9fa6-7596832fb2a3@redhat.com> <11b1c25b-3e20-4acf-9be5-57b508266c5b@redhat.com> <89e04df9-6a2f-409c-ae7d-af1f91d0131e@arm.com> <789cb7e4-8659-4244-b72e-e8fa0b26431d@arm.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: <789cb7e4-8659-4244-b72e-e8fa0b26431d@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: EB50718001C X-Stat-Signature: ofzcoajrg79maw9m7raei7dx7k3p1ek7 X-Rspam-User: X-HE-Tag: 1713867529-377284 X-HE-Meta: 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 ekYl3s1m VW8JXBnccFM0u1PaPJC0fuoPShj3dfkXcxrR2fKovNZDymyTc0whADAXqj/sJQJmznKZ+d/BexuUrXjvoX/9cdBp3DdmbH0odAH4r2y/f/huyf75f+83BFtCNZ+C5SSJiPHjLNzjmhGSbko2zi3yRD5cdlB7s3QjNxiCA0OCYNLrsKzDu7AJ70+JW0mBGZL2zsM+UjI8eVdpbAECwvL2PaELbajGpeY1eDgBkK92uStpk8X34ETGMS+uoSiuXy/V9Ala5PFEkBb6mmJSiLRl/ajFXQSHN9eXbBpValU7lIYJkvSs1C2d/Us5D+QaXOv+PkXYHQ6n36Tq6x86B5ACEgeZFEvUD9TWyrvGJ8SJwYEwUrN6UsIcslyaR5A== 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 23.04.24 12:15, Ryan Roberts wrote: > Hi David, > > Sorry for the slow reply on this; its was due to a combination of thinking a bit > more about the options here and being out on holiday. > No worries, there are things more important in life than ptep_get_lockless() :D >> (1) seems like the easiest thing to do. > > Yes, I'm very much in favour of easy. > >> >>> >>> Perhaps its useful to enumerate why we dislike the current ptep_get_lockless()? >> >> Well, you sent that patch series with "that aims to reduce the cost and >> complexity of ptep_get_lockless() for arm64". (2) and (3) would achieve that. :) > > Touche! I'd half forgotten that we were having this conversation in the context > of this series! > > I guess your ptep_get_gup_fast() approach is very similar to > ptep_get_lockless_norecency()... So we are back to the beginning :) Except that it would be limited to GUP-fast :) > > But ultimately I've come to the conclusion that it is easy to reason about the > current arm64 ptep_get_lockless() implementation and see that its correct. The > other options both have their drawbacks. Yes. > > Yes, there is a loop in the current implementation that would be nice to get rid > of, but I don't think it is really any worse than the cmpxchg loops we already > have in other helpers. > > I'm not planning to persue this any further. Thanks for the useful discussion > (as always). Make sense to me. let's leave it as is for the time being. (and also see if a GUP-fast user that needs precise dirty/accessed actually gets real) -- Cheers, David / dhildenb