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 611DDC0218F for ; Thu, 30 Jan 2025 15:59:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CDC7C2802AB; Thu, 30 Jan 2025 10:59:28 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C8A702802AA; Thu, 30 Jan 2025 10:59:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B0B042802AB; Thu, 30 Jan 2025 10:59:28 -0500 (EST) 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 912AF2802AA for ; Thu, 30 Jan 2025 10:59:28 -0500 (EST) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 380AC1C53C0 for ; Thu, 30 Jan 2025 15:59:28 +0000 (UTC) X-FDA: 83064578016.01.38C96D5 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf13.hostedemail.com (Postfix) with ESMTP id B4DCF2000F for ; Thu, 30 Jan 2025 15:59:25 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=N7LisbAy; spf=pass (imf13.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=1738252765; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to: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=DsnUIxFI2s6Rz4ZTdh0EYdszbaLS5S9D8bAJj6V8Zjk=; b=Y00RAdeniWyP50Iaowm08Wq4DMqVxI9o0Eg95ZL5QrPQJrzAwLueTJMMAPsh4CFOy1kshL wnzFyurYCxrxfc4ddZ90a86ZCzntFZckGGHn9bAF8P2VlraZa3KvByilgmPZkkWKm2JOnC GsTthUdfC8LEiwtr6xsz/i++y3Ak3YU= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=N7LisbAy; spf=pass (imf13.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-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1738252765; a=rsa-sha256; cv=none; b=KNRBztGJnk/9rKK6GDbRpf83GLllF4kx75iXoIZY9YttrZc0wr//lc+qtqkIganR70+Czj cJTnpJvH7HreRtegZwZGNxzDYJFBdZvv2vredo680alThNeBjNJUzL6PrGddcO3QBrUYXg c6VSj0iXTfbFBNo6sOovv0uikV/OMBI= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1738252765; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to: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=DsnUIxFI2s6Rz4ZTdh0EYdszbaLS5S9D8bAJj6V8Zjk=; b=N7LisbAyqzFTxiSlj+JPBDwvLIjEX8wwESjn7kYaugIF5SAQV8YEbHFJcYh+wTW3nV7QRB CbfSCK1Wz3s4u0HOVT85I4Jqi9v4nS3ONhTf6wf/mCj8WLo6LJwCZqDFzcCV24HNB3XE+G O7/JgRHhJays2AYMaIENTBua2RCsEKQ= 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-610-78z29R_-NTeIR_YcT8C-NQ-1; Thu, 30 Jan 2025 10:59:21 -0500 X-MC-Unique: 78z29R_-NTeIR_YcT8C-NQ-1 X-Mimecast-MFC-AGG-ID: 78z29R_-NTeIR_YcT8C-NQ Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-4362f893bfaso4940915e9.1 for ; Thu, 30 Jan 2025 07:59:21 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1738252760; x=1738857560; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:to:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=DsnUIxFI2s6Rz4ZTdh0EYdszbaLS5S9D8bAJj6V8Zjk=; b=Djt4+Q3gzqQOFVlv0qrH3EMWl48iNJ63LobuJU7Db+gxpzGiG3UFQzyrOSw1F8YyR3 2gD/H7zjg0MZUy1BHO9ayBBe17e1AxhbZ7GR2tL5ZqVpt8wZHh9rWMvoJHiY07sWSuwA fYLa0hATLXQozVk74P+eb1g5i5lW7mlq2IJopZOTAnyHGmCU99QJsOiCrlE4hVXHtYoy JFBa3EqXgXTx1HDTQUB7HR3Xa2zf9uyvO3Q4V9uFpv9Uvgwp+Xl/2WV60iNH0MiTsw2H 42qU7tRqr4FplBFy6ofnGswk7O3F9gAfhJVx0lIDN3O0L2hTtB6jIWnh+VCBrrfbnf2v ZOxA== X-Forwarded-Encrypted: i=1; AJvYcCWYAtNIyC1pDBCfX0oO+3BlAIVswiGgJjcT3u/kZrXrz7FS66le2H9iieV4jDKXC9XZYbD9mVq8Bg==@kvack.org X-Gm-Message-State: AOJu0YzKo1d0tt0AMe/Fcit+97pIySjj55cbpcMsj5PvomIw5Q8K33a3 HjV/tiezP3Ta7qgDRlRxSMXy0AWA8BM8nUKDcZ+wvQTjAiLOf2ZsXX3LwYUFvybIRHsQrycfdzM CkE5veGO2vNmi+3PhnhZYzB683hKqQ62likiwakue0zD3qd35 X-Gm-Gg: ASbGnct9wX8TpybnD8nSdHbLHZnbjzJb3eeiAKqVMgV+cZGI0UfbF6xZ1Wva0Vor8hi zdFZKhlK78FeGAh/tFo6ZY2pDtnVECg8O0AJoTE3bUd1XmJEtYy1VXqyRKJ6A6oL39rPxYU5AxA yYKeGHXe50dYzYZqWYNJ1U1wn24B3ThuBV0AEw6pZ/6V/VbgLbb5/H7on1iWQSDGGhTchWJbVvX 8KVg6waV/A29Z1kHu2slEMFPxUyZqnIXmiVgNgdOINem9egbhxjhfqbEdZsUtAlBWDew8SvEr9H XXvEev+uMyyDVE5BCPobNFmWma3nqpBusgOq1GoeeERpIzWeOKeEcaGW1rozW/rFO0HAaV8vhy1 idBO64t+7tFtaSweFFMiP5Rpm932+dE0l X-Received: by 2002:a05:600c:4e52:b0:434:9dfe:20e6 with SMTP id 5b1f17b1804b1-438dc3fc2b0mr67980845e9.23.1738252760133; Thu, 30 Jan 2025 07:59:20 -0800 (PST) X-Google-Smtp-Source: AGHT+IG3rx1FCxTfK9dT4GZUYFii4gIoyAgygN9uLXGcwSeyv5w8U63P6tIrS8/LxKqXr0qRCsRl9g== X-Received: by 2002:a05:600c:4e52:b0:434:9dfe:20e6 with SMTP id 5b1f17b1804b1-438dc3fc2b0mr67980555e9.23.1738252759687; Thu, 30 Jan 2025 07:59:19 -0800 (PST) Received: from ?IPV6:2003:cb:c713:3b00:16ce:8f1c:dd50:90fb? (p200300cbc7133b0016ce8f1cdd5090fb.dip0.t-ipconnect.de. [2003:cb:c713:3b00:16ce:8f1c:dd50:90fb]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438e245f41esm27323025e9.36.2025.01.30.07.59.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jan 2025 07:59:18 -0800 (PST) Message-ID: <9f59b475-232f-41d4-bd6f-7f84111062ac@redhat.com> Date: Thu, 30 Jan 2025 16:59:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 04/12] mm/rmap: implement make_device_exclusive() using folio_walk instead of rmap walk To: Alistair Popple , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Jason Gunthorpe References: <20250129115411.2077152-1-david@redhat.com> <20250129115411.2077152-5-david@redhat.com> <7tzcpx23vufmp5cxutnzhjgdj7kwqrw5drwochpv5ern7zknhj@h2s6y2qjbr3f> <54a55ff7-38c8-42c2-886f-d6d1985072a9@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: JTDAQNLg4hfIXUo51cqb9NnIbGMw2HRx_lWJvnF7oP8_1738252760 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: rspam02 X-Rspamd-Queue-Id: B4DCF2000F X-Stat-Signature: 84a3iexhu3zcdesxfnsrwdq1wge3t55z X-Rspam-User: X-HE-Tag: 1738252765-666410 X-HE-Meta: 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 iMCMOxCr kNmZ8OtNLYp1tQQg+zrc+AljicPGx6vtRbT72nPaFRTJ9hTUYY8AhEbUg1/zXNUShXrl/dLBRLWEQqAg//FVtVWBdhLeCu9coisUhihkNC1Imb/rNMqQKc01Asc5BlU9RXFlOAOb6IUWGj9io9FzAC/eHvTTClAVXRV6IGWoIKz21DnNOJh3ZjojH5AF6aXS4SYDNUltzon/XSJaBfRS1bqtQWxPraqKsUBkz85LhiAq7UoKPn2AeaQaR901/tVYH+ZZ7kUDezCaa+tO7OHqrPO9ioY1LhonYsuxddq8dU8hNZDxMway5UCkCbEYO+3v0wNM+Qm5GXLSTe5ojUvPpNLNEvrsB9fVdyaXmEnX9Q2wFLyjKLL+3GejEzsUHpp3ZsH2Fn42RJxAAvNokj+dmcIbDSVm70Us/orC3UK4B304rsiIBPg+8HOhDZuj8Uc4rZaCm 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: >>>>> Note that the PTE is >>>>> always writable, and we can always create a writable-device-exclusive >>>>> entry. >>>>> >>>>> With this change, device-exclusive is fully compatible with THPs / >>>>> large folios. We still require PMD-sized THPs to get PTE-mapped, and >>>>> supporting PMD-mapped THP (without the PTE-remapping) is a different >>>>> endeavour that might not be worth it at this point. >>> >>> I'm not sure we actually want hugepages for device exclusive, since it has >>> an impact on what's allowed and what not. If we only ever do 4k entries >>> then userspace can assume that as long atomics are separated by a 4k page >>> there's no issue when both the gpu and cpu hammer on them. If we try to >>> keep thp entries then suddenly a workload that worked before will result >>> in endless ping-pong between gpu and cpu because the separate atomic >>> counters (or whatever) now all sit in the same 2m page. >> >> Agreed. And the conversion + mapping into the device gets trickier. >> >>> >>> So going with thp might result in userspace having to spread out atomics >>> even more, which is just wasting memory and not saving any tlb entries >>> since often you don't need that many. >>> >>> tldr; I think not supporting thp entries for device exclusive is a >>> feature, not a bug. >> >> So, you agree with my "different endeavour that might not be worth it" >> statement? > > Yes. > > Well I think we should go further and clearly document that we > intentionally return split pages. Because it's part of the uapi contract > with users of all this. Yes, see my reply to patch #3/ > > And if someone needs pmd entries for performance or whatever, we need two > things: > > a) userspace must mmap that memory as hugepage memory, to clearly signal > the promise that atomics are split up on hugepage sizes and not just page > size > > b) we need to extend make_device_exclusive and drivers to handle the > hugetlb folio case > > I think thp is simply not going to work here, it's impossible (without > potentially causing fault storms) to figure out what userspace might want. Right, I added a link to this discussion in the patch. Thanks! -- Cheers, David / dhildenb