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 C16F2CD11DF for ; Tue, 26 Mar 2024 17:39:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4BB946B0083; Tue, 26 Mar 2024 13:39:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 46B866B0088; Tue, 26 Mar 2024 13:39:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2E5096B008A; Tue, 26 Mar 2024 13:39:32 -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 1EE016B0083 for ; Tue, 26 Mar 2024 13:39:32 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id E98631604AD for ; Tue, 26 Mar 2024 17:39:31 +0000 (UTC) X-FDA: 81939902142.13.27A1C93 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf05.hostedemail.com (Postfix) with ESMTP id AACE810000B for ; Tue, 26 Mar 2024 17:39:29 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="c/puSwB4"; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf05.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1711474769; 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=nv03yiZAiZgBWj6kUmes+WMp8CfflptuZICYst0uZlA=; b=Vvq/c9ueaE3az073YF6GDaCyYPPHTW983seCkZEWSWwg3GaULsRHEeOfnJI5opdP03oHNv OS6J8MFF8mEXcYhWRBFAgQDbUOu4k1LJraJUlKU6GRC9DDqdO9YfqlVEzkKXgQ8Nz0jwhj FLhd4Lq2xLSHBX+yjllQOCN/Ka97u3A= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="c/puSwB4"; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf05.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1711474769; a=rsa-sha256; cv=none; b=s+DT4J0C/yGdUMYoYJNs1h5K0zWKkR9edW3XpCMG+nKQGx1lR5FNLZ6L9s0dJLC7Z2Rw+Q v1ng+aljtg6ji3DrH9IQNKwxEnnHj/SvLorSzk2dfMavid+EquWN+h+53d3BbEg0GqYSOk azW8McE8mKPBqEZTSZGr9ke9hwzL6hE= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1711474769; 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=nv03yiZAiZgBWj6kUmes+WMp8CfflptuZICYst0uZlA=; b=c/puSwB4qf1pbBmWSDM1+d7lB/lYnth15LXTtzw6K8B0sH25EPxI+6wJHcKqTlx0HxJVrt Km7X+YiOFXGey9MYGtPteQBuv60NiPG8/20o620NCoeypdV3YQlkAAPuNJGasbtVey2oWo h/xDjXqBUJlmHDEjblciEQlsIMl8Ink= 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-446-j2qB902yOsS0kymy78z67A-1; Tue, 26 Mar 2024 13:39:27 -0400 X-MC-Unique: j2qB902yOsS0kymy78z67A-1 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-33ed5ddd744so1759391f8f.3 for ; Tue, 26 Mar 2024 10:39:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1711474765; x=1712079565; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :references:cc:to:content-language:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=nv03yiZAiZgBWj6kUmes+WMp8CfflptuZICYst0uZlA=; b=S8Fi4MUC6LQFs35SFi5E87zbT6COvCQuFSbN5Es6/tbKabW7yFnotZ8sa7YjTdcwCH H7+/yWsolsx/XUaJqsC/jQKx3lcobpE6SRoX4O0T9aaNHgl0+1ebKq0DaUATB851sx1C vonOb5wnJfh6S1YOZiRIQCa9oJ9n0E5aVea/baEVhcMOaGVP7yg1C23HHWxmYuSl5rLC 4v3EzDpjNnCCwa49obAUDeV8BFs8leuGZJFS6YCZ9WG4BAAlcga7suNFTdBPFqoBp369 X0fg3qFt0Z3otHRVXcCNegoIimdz0yHGLdrQmjO+aBp3rW4fzo/U/S/kiURBA1bUiA80 xWRw== X-Forwarded-Encrypted: i=1; AJvYcCUW+oMk2e/pz5726u08Bf742uI+ppdNWUbUct/ux5yolm8ZNoL3dbtJG2rwZ+yeInivBdmFzNFu8vEJRqw1/B1r2gQ= X-Gm-Message-State: AOJu0YxV0AGS01xu6StRLusahlWULRoiMwRYhzkM7l8AJ5Zs9M6Z0AJY y5pjgthp4J7dtAksViTLka+6v59PwwTSISnsYCBmx0R34w1+DSFKbYuvSylNhgZqXRTYKJSiqso R2GA2luAvyL8ceoKd2eUKOngphoHlea8hHQTX+3g1RAognNBg X-Received: by 2002:a5d:4805:0:b0:33e:d507:102c with SMTP id l5-20020a5d4805000000b0033ed507102cmr8230438wrq.11.1711474765396; Tue, 26 Mar 2024 10:39:25 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGStmoliOBFqeiRbrZbk5TvArv1+lSuTgwJ1I7RRDcv7W8w9W+B1NMLOzhmqi9G2xd7QQXHKw== X-Received: by 2002:a5d:4805:0:b0:33e:d507:102c with SMTP id l5-20020a5d4805000000b0033ed507102cmr8230414wrq.11.1711474764893; Tue, 26 Mar 2024 10:39:24 -0700 (PDT) Received: from [192.168.3.108] (p5b0c6b40.dip0.t-ipconnect.de. [91.12.107.64]) by smtp.gmail.com with ESMTPSA id cr8-20020a05600004e800b0033e7715bafasm12736164wrb.59.2024.03.26.10.39.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Mar 2024 10:39:24 -0700 (PDT) Message-ID: <8bd9e136-8575-4c40-bae2-9b015d823916@redhat.com> Date: Tue, 26 Mar 2024 18:39:23 +0100 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> <0ae22147-e1a1-4bcb-8a4c-f900f3f8c39e@redhat.com> <374d8500-4625-4bff-a934-77b5f34cf2ec@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: 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-Rspam-User: X-Stat-Signature: 693ss7pggetzbrz5joey6s6q6oeg6qm4 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: AACE810000B X-HE-Tag: 1711474769-58473 X-HE-Meta: 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 iEX31F8s 26M+NIGNJAvTeMoKO62d9RtcwS2EbJ7bUHqh1qPb5TzXsu3OswieRIyAJGWTmH9up86oN9kYOLsZ3eBAiVS9JYdey2zuqhnW/8sDoONrsREini2M4krFhvof3+M7plvF3S9MHjOYduUQuESIL1RlnECWEzEF3uSWf1WUmJ83MgsPlroSWRKqYAVpA0v3rem2TKZ3zSIFi2cZMgDjf0tvDl069Z6nglWqIer7IDBlzxcjXfOOEEP/P+4oI7h2bO8wyvdEQYWdZ+YuRUj+Q0h0ojWYk1Vom6N43omhf6nazw47TpLszbSlLYP7wdOPfnUie8fSpweZKWYFx+U2mU+Nwmlyyq8HFS5uXUL+tP0bq0h5lTFlQTtDddkM0c6t/WoiX8fU/aaW8Dr/FKas= 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 26.03.24 18:32, Ryan Roberts wrote: > On 26/03/2024 17:04, David Hildenbrand wrote: >>>>>> >>>>>> Likely, we just want to read "the real deal" on both sides of the pte_same() >>>>>> handling. >>>>> >>>>> Sorry I'm not sure I understand? You mean read the full pte including >>>>> access/dirty? That's the same as dropping the patch, right? Of course if we do >>>>> that, we still have to keep pte_get_lockless() around for this case. In an >>>>> ideal >>>>> world we would convert everything over to ptep_get_lockless_norecency() and >>>>> delete ptep_get_lockless() to remove the ugliness from arm64. >>>> >>>> Yes, agreed. Patch #3 does not look too crazy and it wouldn't really affect any >>>> architecture. >>>> >>>> I do wonder if pte_same_norecency() should be defined per architecture and the >>>> default would be pte_same(). So we could avoid the mkold etc on all other >>>> architectures. >>> >>> Wouldn't that break it's semantics? The "norecency" of >>> ptep_get_lockless_norecency() means "recency information in the returned pte may >>> be incorrect". But the "norecency" of pte_same_norecency() means "ignore the >>> access and dirty bits when you do the comparison". >> >> My idea was that ptep_get_lockless_norecency() would return the actual result on >> these architectures. So e.g., on x86, there would be no actual change in >> generated code. > > I think this is a bad plan... You'll end up with subtle differences between > architectures. > >> >> But yes, the documentation of these functions would have to be improved. >> >> Now I wonder if ptep_get_lockless_norecency() should actively clear >> dirty/accessed bits to more easily find any actual issues where the bits still >> matter ... > > I did a version that took that approach. Decided it was not as good as this way > though. Now for the life of me, I can't remember my reasoning. Maybe because there are some code paths that check accessed/dirty without "correctness" implications? For example, if the PTE is already dirty, no need to set it dirty etc? -- Cheers, David / dhildenb