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 B2AABC02181 for ; Fri, 24 Jan 2025 10:44:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DBC3228005B; Fri, 24 Jan 2025 05:44:39 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D6A3E280059; Fri, 24 Jan 2025 05:44:39 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C0AEA28005B; Fri, 24 Jan 2025 05:44:39 -0500 (EST) 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 A344A280059 for ; Fri, 24 Jan 2025 05:44:39 -0500 (EST) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 550921C82B7 for ; Fri, 24 Jan 2025 10:44:39 +0000 (UTC) X-FDA: 83042011878.25.499E656 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf04.hostedemail.com (Postfix) with ESMTP id CDC6840002 for ; Fri, 24 Jan 2025 10:44:36 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Hh0VZDn6; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1737715477; a=rsa-sha256; cv=none; b=wyq9vc8c3c9ekBGaBwcqlzMVNA+SQpE6WrUWgtBkfVUK1nzjKBVaSFP3lzDUoC5ncGHGZn MuSfMSu0fMbz/o4gUMCCB2xwvyWUTfPtGzdXQdMB70YKvoC3wZTt8nGKO6SCcY0eQqu9Mu wtyLkItrLR8eV/XhFOce3q5Cn2Cz3X0= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Hh0VZDn6; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 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=1737715477; 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=9LGicVHjVXKCgFdIoAFwldRTveMxoGLLdTcV9/dVeF4=; b=Ghb71U8ce4bbM5SoOaLTzroBz9g4EvhiDzV1rca3ssquw43u5J8dJXO74rYpGWLbNfsarC g+zlmhWR6Ardqb17QU7PODLBnq++33SR0wtmGDr0V8Y8LK/EcYXvGfE9hNQmPH8Kfpf62R vhnU+dHlDcTlaOIdZoPB11fqr3GvQR0= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1737715476; 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=9LGicVHjVXKCgFdIoAFwldRTveMxoGLLdTcV9/dVeF4=; b=Hh0VZDn6vfNzXMM23UojOSK9LPYOuq1nlJiFVl6CYH3dPHDVjAu6ssMVTYmPtRRYmkGHEC N2PVU6vmbqSF9ucYa7BGuDQWpN3V5wLHO875591iF/H9WfknkxkY2sByeeN2nzEn9q3kxb sFmp2n1i9Ni4j7Cl8ljaRtoKnIobeig= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-497-NyQiZLNnOTiIHJXfvLI3Hw-1; Fri, 24 Jan 2025 05:44:32 -0500 X-MC-Unique: NyQiZLNnOTiIHJXfvLI3Hw-1 X-Mimecast-MFC-AGG-ID: NyQiZLNnOTiIHJXfvLI3Hw Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-4362b9c15d8so9062345e9.3 for ; Fri, 24 Jan 2025 02:44:32 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1737715472; x=1738320272; 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=9LGicVHjVXKCgFdIoAFwldRTveMxoGLLdTcV9/dVeF4=; b=jTf6OoqXgvDaKJ2sC4KUA8oVFQxNp4oJuKx+kujZdSOHl7/Xgrp3spbu3tINAQa45R nZEunio7sq05nxD5RuVeq5gWMNKmJYjPxcnb5ILj54XaGt4d691Kwmfz6iOqc2ztp156 qnCwed274k9qEZ34oU3rq08WeKBDcdNvLAa3YTDfi4vduO+8oA6hf600E7QSLl2Wn3N7 gp231IJVCCUJgf/lyI5Uio3XvcJX3Nv67tl8KNS633op68VP0643+/o6BKe7ffEQuJLe XaMywYuh0qO3i3oIIwwWSW4D5tiWORNvsIr9tWnRR9esaQEyLrZt07APrWLJUnScONO1 N2Cw== X-Gm-Message-State: AOJu0Yzs7/PWtIm2XzpkXqIDB7r38u6768XSV4CUVTsOodaLReY/PETx vJtcth9TqpWBBm4Rf7QTMjrzH/huIszyDwb2GATyRpJwHeb4LUqdsGPK4Ggx9YZfYZUJBPDeKKz a6tUSoym3ulk9euEf+0w32Lpi6t/aB1M1IryeZ0lOCDtkC0aYwIBR3KS4TNCraCeE5Je6YxotCr lyNWuZ9OevFeM0/AFsLPclkCdIHXO1jhG5qA== X-Gm-Gg: ASbGncts+mYKPkp3vHHMs2IUqtrUDvLfoQumsKoPcNLBnw4FHl9UJlHPDdY9Ffk+WBg IT8J0nZMczOiRYwTn/Nz/Wt97qotfKOl74Bnst21W4JqU6KvGNsjwJS0P/6KZVLGFbKt2A/igTG awkKXO5BJ6OSRm1jpfSFq2qjYEpVLnjQBvWS9L2R1n5slV3wy93NQ+sEVUWckpUkTYhmKHQcFuS UHq5SBzKvCZjzaa/hFk6uoL6Gk0GfgGJFQhJ1PHBPyCEeig205eNK4Kt+A40Wp6XA6URNzK40Cu Pe8vjkLeelnrVCw0Sx33v1Pyb4Fi X-Received: by 2002:adf:fd84:0:b0:385:faf5:eb9f with SMTP id ffacd0b85a97d-38bf57c91e7mr28813777f8f.48.1737715471643; Fri, 24 Jan 2025 02:44:31 -0800 (PST) X-Google-Smtp-Source: AGHT+IEKstrH5UL8LgQDwA4DkXTRFLjT6VqmqvDWzIKYlE7kR/ewYGg5Hi2VcNrw25AxqdO1qrWvQg== X-Received: by 2002:adf:fd84:0:b0:385:faf5:eb9f with SMTP id ffacd0b85a97d-38bf57c91e7mr28813740f8f.48.1737715471211; Fri, 24 Jan 2025 02:44:31 -0800 (PST) Received: from ?IPV6:2a09:80c0:192:0:5dac:bf3d:c41:c3e7? ([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c2a18931esm2342703f8f.60.2025.01.24.02.44.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Jan 2025 02:44:30 -0800 (PST) Message-ID: <8c6f3838-f194-4a42-845d-10011192a234@redhat.com> Date: Fri, 24 Jan 2025 11:44:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Question] Are "device exclusive non-swap entries" / "SVM atomics in Nouveau" still getting used in practice? To: "linux-mm@kvack.org" , John Hubbard , nouveau@lists.freedesktop.org, Jason Gunthorpe , Alistair Popple , DRI Development , Karol Herbst , Lyude Paul , Danilo Krummrich References: <346518a4-a090-4eaa-bc04-634388fd4ca3@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: D2bk7JwBlCQCKzmr5aWAGcKmLXuhvqRi1UeCyR7nyOI_1737715472 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: rspam04 X-Rspamd-Queue-Id: CDC6840002 X-Stat-Signature: qo4ouyq9f4qaq4k1r9uposqdrmrep6jb X-Rspam-User: X-HE-Tag: 1737715476-340065 X-HE-Meta: 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 C8P5/4ZH 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 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 23.01.25 16:08, Simona Vetter wrote: > On Thu, Jan 23, 2025 at 11:20:37AM +0100, David Hildenbrand wrote: >> Hi, >> >> I keep finding issues in our implementation of "device exclusive non-swap >> entries", and the way it messes with mapcounts is disgusting. >> >> As a reminder, what we do here is to replace a PTE pointing to an anonymous >> page by a "device exclusive non-swap entry". >> >> As long as the original PTE is in place, the only CPU can access it, as soon >> as the "device exclusive non-swap entry" is in place, only the device can >> access it. Conversion back and forth is triggered by CPU / device faults. >> >> I have fixes/reworks/simplifications for most things, but as there is only a >> "real" single user in-tree of make_device_exclusive(): >> >> drivers/gpu/drm/nouveau/nouveau_svm.c >> >> to "support SVM atomics in Nouveau [1]" >> >> naturally I am wondering: is this still a thing on actual hardware, or is it >> already stale on recent hardware and not really required anymore? >> >> >> [1] https://lore.kernel.org/linux-kernel//6621654.gmDyfcmpjF@nvdebian/T/ > Thanks for your answer! Nvidia folks told me on a different channel that it's still getting used. > As long as you don't have a coherent interconnect it's needed. On intel > discrete device atomics require device memory, so they need full hmm > migration (and hence wont use this function even once we land intel gpu > svm code in upstream). Makes sense. > On integrated the gpu is tied into the coherency > fabric, so there it's not needed. > > I think the more fundamental question with both this function here and > with forced migration to device memory is that there's no guarantee it > will work out. Yes, in particular with device-exclusive, it doesn't really work with THP and is only limited to anonymous memory. I have patches to at least make it work reliably with THP. Then, we seem to give up too easily if we cannot lock the folio when wanting to convert to device-exclusive, which also looks rather odd. But well, maybe it just works good enough in the common case, or there is some other retry logic that makes it fly. > At least that's my understanding. And for this gpu device > atomics without coherent interconnect idea to work, we'd need to be able > to guarantee that we can make any page device exclusive. So from my side I > have some pretty big question marks on this entire thing overall. I don't think other memory (shmem/file/...) is really feasible as soon as other processes (not the current process) map/write/read file pages. We could really only handle if we converted a single PTE and that PTE is getting converted back again. There are other concerns I have (what if the page is pinned and access outside of the user space page tables?). Maybe there was not need to handle these cases so far. So best I can do is make anonymous memory more reliable with device-exclusive and fixup some of the problematic parts that I see (e.g., broken page reclaim, page migration, ...). But before starting to cleanup+improve the existing handling of anonymous memory, I was wondering if this whole thing is getting used at all. -- Cheers, David / dhildenb