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 11F82C4167B for ; Fri, 1 Dec 2023 09:23:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7D5088D0069; Fri, 1 Dec 2023 04:23:46 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7848A8D0001; Fri, 1 Dec 2023 04:23:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5FD858D0069; Fri, 1 Dec 2023 04:23:46 -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 4F6518D0001 for ; Fri, 1 Dec 2023 04:23:46 -0500 (EST) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 1E3AA1A0161 for ; Fri, 1 Dec 2023 09:23:46 +0000 (UTC) X-FDA: 81517712052.14.42AF936 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf28.hostedemail.com (Postfix) with ESMTP id CA865C0008 for ; Fri, 1 Dec 2023 09:23:43 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aYXbPUjW; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf28.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=1701422624; 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=J/HNsGBAY9tCftPYDhpctNf5+8xRFRhgnlekGos4DSM=; b=BxwNy7dFdY2A/8W+l+xRD4w2u1SySLGp5Y+4/cdYoY4elP/lnF0R6uTGLkIjoxCSxNxTQJ AntxuAZhAHZikmqjeOcK2DSSRkhb51bgoRJ13TdS9Snrxl5+GxAf0imIKLW6wON1LGFf+g MyOulRjs07ooHvT67pQPwhd//H/TZHs= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aYXbPUjW; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf28.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=1701422624; a=rsa-sha256; cv=none; b=uVu4jz8tEucIquhBRY//3Ac99utZ8wv1kYgLW9dCwkTZgbPIeScPm5KlmJfOTv04ZGfmDI QZvn+wzeLi9yxdpN1jPXv1Se+0DvIs5WHj7+k/m4un7zlxm/K+bgLQPiRC9e9efepjlrsC rmnLzSGLLAdnTlrIGFD3sjb5faJydkM= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1701422623; 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=J/HNsGBAY9tCftPYDhpctNf5+8xRFRhgnlekGos4DSM=; b=aYXbPUjWch9Wgrvr8vPs8c1TJTA/hWj4C44aDYwXyFPmfI0yFx0sAB8rm70nOxQkGpixJS QCRlNxT4NFC40eLUCYhG9MK6XIKHY7orLqUl7Qrzl5gLUrezanXaJsGOCx5wJAiXD+onpx Rsa4zwJKJvoJucYSby0F98fc55QvA5Q= 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-315-e-v-ECisOfmfBq13O9MARQ-1; Fri, 01 Dec 2023 04:23:41 -0500 X-MC-Unique: e-v-ECisOfmfBq13O9MARQ-1 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-40b3519a03aso16036215e9.3 for ; Fri, 01 Dec 2023 01:23:41 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701422620; x=1702027420; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language: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=J/HNsGBAY9tCftPYDhpctNf5+8xRFRhgnlekGos4DSM=; b=s1D7umVSqy0G01EFhX9awufiAjEhagT1VTtkWOuDtxkygMLdXKvc66lbZGfY8scfMf pl9AnARrspQ15/Q0gHPEH1kpb9PW1v8bgBmA5ngoUu29ytuC9UXhcIFb40yOxPluXCfJ JAh1gIB4s6+RX9liN3bEf2MSD7nz2kcO5akx8oSJBxAjch3n2gt7oX6+O2nRXNaqt1Kr TIrNgX3W3D6PVb4f2Orf0E24hbCCC4XwQXeGl3vtfCSPi7w2kYHlUuMJfTW+Ykb3kiEx Rifoh06+Gog+hi6Hg8Ikq52Wjtz0eVWaohqLKXNdGic2tpTN8QYyKNuxohZD6ZnWzlaJ 9OZg== X-Gm-Message-State: AOJu0YwhJCOn7XyUE3XlAvOre3XcDwCVe1aYcMNN4CjkLAqxJ3YRw08c 5wRUOWpPAO/KltnUEJl2FBY+fpNHgCleGMAcejBWKtlPyM0Lfp1dxjHt5sdXwd+3LK0nOtopNJf gZ+loM+HyTeI= X-Received: by 2002:a05:600c:1da7:b0:40b:5e59:cca0 with SMTP id p39-20020a05600c1da700b0040b5e59cca0mr256582wms.129.1701422620570; Fri, 01 Dec 2023 01:23:40 -0800 (PST) X-Google-Smtp-Source: AGHT+IFbj59aKrdp1bwC45vVYTH//o6ADwu3HnhrokcgPLEaEt76aIWUxif6MnQKy43m6yymBTuLpg== X-Received: by 2002:a05:600c:1da7:b0:40b:5e59:cca0 with SMTP id p39-20020a05600c1da700b0040b5e59cca0mr256570wms.129.1701422620020; Fri, 01 Dec 2023 01:23:40 -0800 (PST) Received: from ?IPV6:2003:cb:c726:4100:c308:78e3:8f80:52ac? (p200300cbc7264100c30878e38f8052ac.dip0.t-ipconnect.de. [2003:cb:c726:4100:c308:78e3:8f80:52ac]) by smtp.gmail.com with ESMTPSA id k18-20020a05600c1c9200b0040b38292253sm8469404wms.30.2023.12.01.01.23.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Dec 2023 01:23:39 -0800 (PST) Message-ID: Date: Fri, 1 Dec 2023 10:23:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/6] mm/gmem: add arch-independent abstraction to track address mapping status To: Weixi Zhu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org Cc: weixi.zhu@openeuler.sh, mgorman@suse.de, jglisse@redhat.com, rcampbell@nvidia.com, jhubbard@nvidia.com, apopple@nvidia.com, mhairgrove@nvidia.com, ziy@nvidia.com, alexander.deucher@amd.com, christian.koenig@amd.com, Xinhui.Pan@amd.com, amd-gfx@lists.freedesktop.org, Felix.Kuehling@amd.com, ogabbay@kernel.org, dri-devel@lists.freedesktop.org, jgg@nvidia.com, leonro@nvidia.com, zhenyuw@linux.intel.com, zhi.a.wang@intel.com, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, tvrtko.ursulin@linux.intel.com References: <20231128125025.4449-1-weixi.zhu@huawei.com> <20231128125025.4449-3-weixi.zhu@huawei.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: <20231128125025.4449-3-weixi.zhu@huawei.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-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: CA865C0008 X-Stat-Signature: ijbnpmiamymr35a9es6uamjuf7s5c7s9 X-HE-Tag: 1701422623-952602 X-HE-Meta: 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 +78I/Ds8 /F52fmO8YxX8al4IJU7+47ogqtXJzRkaFpCxtMmKndBhAEsDW1C6o+PxTIlaqddvH0TYGj3WXbhZdzGmy+RJ14TACbrO1BTD/mpKWFU0P7UPRqXtSo2YIAGCcUl2kWxNVK7Uo0heuGvcOs0OjkWVsZ8Tx48/QPFAnesZdo8qm1hHKkf9UoQHU7AjMjMj1zfE5luPrV0mNMS60w8AqH9lVRQUau+RnigHwmDBziElcXW4sjmfpO9FCYKU4AfpRBTlZvJ0pYPXU2UT35dMejXNV65eP+c8DVG4zbz9/5x9mMwxE0pK+EH6y7fcGrhSlVqdc8mNYK8GusEK5D0Lmx9LrpKMP9ofvICerOYGb1CfnmHCV0aqafSDOg9nOATilRoKZbC0AdpTuwR50qwRg/mFksw3/PnjTLZfF+xjWT0zdeHI5WzHAw2FPmxqYMY0kT7RI5H5i6RslPp78ti0RJHPJi0PnQUbelsY3PKTsRbJ+dD6/tGE= 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 28.11.23 13:50, Weixi Zhu wrote: > This patch adds an abstraction layer, struct vm_object, that maintains > per-process virtual-to-physical mapping status stored in struct gm_mapping. > For example, a virtual page may be mapped to a CPU physical page or to a > device physical page. Struct vm_object effectively maintains an > arch-independent page table, which is defined as a "logical page table". > While arch-dependent page table used by a real MMU is named a "physical > page table". The logical page table is useful if Linux core MM is extended > to handle a unified virtual address space with external accelerators using > customized MMUs. Which raises the question why we are dealing with anonymous memory at all? Why not go for shmem if you are already only special-casing VMAs with a MMAP flag right now? That would maybe avoid having to introduce controversial BSD design concepts into Linux, that feel like going a step backwards in time to me and adding *more* MM complexity. > > In this patch, struct vm_object utilizes a radix > tree (xarray) to track where a virtual page is mapped to. This adds extra > memory consumption from xarray, but provides a nice abstraction to isolate > mapping status from the machine-dependent layer (PTEs). Besides supporting > accelerators with external MMUs, struct vm_object is planned to further > union with i_pages in struct address_mapping for file-backed memory. A file already has a tree structure (pagecache) to manage the pages that are theoretically mapped. It's easy to translate from a VMA to a page inside that tree structure that is currently not present in page tables. Why the need for that tree structure if you can just remove anon memory from the picture? > > The idea of struct vm_object is originated from FreeBSD VM design, which > provides a unified abstraction for anonymous memory, file-backed memory, > page cache and etc[1]. :/ > Currently, Linux utilizes a set of hierarchical page walk functions to > abstract page table manipulations of different CPU architecture. The > problem happens when a device wants to reuse Linux MM code to manage its > page table -- the device page table may not be accessible to the CPU. > Existing solution like Linux HMM utilizes the MMU notifier mechanisms to > invoke device-specific MMU functions, but relies on encoding the mapping > status on the CPU page table entries. This entangles machine-independent > code with machine-dependent code, and also brings unnecessary restrictions. Why? we have primitives to walk arch page tables in a non-arch specific fashion and are using them all over the place. We even have various mechanisms to map something into the page tables and get the CPU to fault on it, as if it is inaccessible (PROT_NONE as used for NUMA balancing, fake swap entries). > The PTE size and format vary arch by arch, which harms the extensibility. Not really. We might have some features limited to some architectures because of the lack of PTE bits. And usually the problem is that people don't care enough about enabling these features on older architectures. If we ever *really* need more space for sw-defined data, it would be possible to allocate auxiliary data for page tables only where required (where the features apply), instead of crafting a completely new, auxiliary datastructure with it's own locking. So far it was not required to enable the feature we need on the architectures we care about. > > [1] https://docs.freebsd.org/en/articles/vm-design/ In the cover letter you have: "The future plan of logical page table is to provide a generic abstraction layer that support common anonymous memory (I am looking at you, transparent huge pages) and file-backed memory." Which I doubt will happen; there is little interest in making anonymous memory management slower, more serialized, and wasting more memory on metadata. Note that you won't make many friends around here with statements like "To be honest, not using a logical page table for anonymous memory is why Linux THP fails compared with FreeBSD's superpage". I read one paper that makes such claims (I'm curious how you define "winning"), and am aware of some shortcomings. But I am not convinced that a second datastructure "is why Linux THP fails". It just requires some more work to get it sorted under Linux (e.g., allocate THP, PTE-map it and map inaccessible parts PROT_NONE, later collapse it in-place into a PMD), and so far, there was not a lot of interest that I am ware of to even start working on that. So if there is not enough pain for companies to even work on that in Linux, maybe FreeBSD superpages are "winning" "on paper" only? Remember that the target audience here are Linux developers. But yeah, this here is all designed around the idea "core MM is extended to handle a unified virtual address space with external accelerators using customized MMUs." and then trying to find other arguments why it's a good idea, without going too much into detail why it's all unsolvable without that. The first thing to sort out if we even want that, and some discussions here already went into the direction of "likely not". Let's see. -- Cheers, David / dhildenb