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Mon, 24 Mar 2025 11:56:50 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGM/QdnX4SaSUQ1lCTAQSBl2+mcQkx9Itz+sJPaIEypWysviQG5vz/qdt1ihvQkuTsBt1Zehw== X-Received: by 2002:a05:620a:2494:b0:7c5:48bc:8c84 with SMTP id af79cd13be357-7c5ba15d8b6mr1595874485a.15.1742842610167; Mon, 24 Mar 2025 11:56:50 -0700 (PDT) Received: from [172.22.33.10] ([99.209.85.25]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c5b9355b19sm540851285a.109.2025.03.24.11.56.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Mar 2025 11:56:49 -0700 (PDT) Message-ID: Date: Mon, 24 Mar 2025 19:56:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] Non-lru page migration in a memdesc world From: David Hildenbrand To: "linux-mm@kvack.org" Cc: "lsf-pc@lists.linux-foundation.org" References: <2612ac8a-d0a9-452b-a53d-75ffc6166224@redhat.com> 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: <2612ac8a-d0a9-452b-a53d-75ffc6166224@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: G6uwfgfQTSiMtEpAYJtQwZ7TRZTD2fLjU7ZhCodMF-M_1742842611 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: rspam09 X-Rspamd-Queue-Id: 7A171A000B X-Stat-Signature: yfttnr1ddgfptj9rwx45s7susje6oioy X-HE-Tag: 1742842613-920292 X-HE-Meta: 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 AlfC4spp 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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 07.01.25 17:11, David Hildenbrand wrote: > Hi, > > one item on my todo list is making PageOffline pages to stop using > "struct page" members except page->type and 1/2 flags, to prepare them > for the memdesc future, to avoid unnecessary atomics, and to resolve > some (so-far) theoretical issues with temporary speculative references. > > For example, the page->_refcount will always be 0 (frozen) for > PageOffline pages, and they will get allocated/freed similar to how we > allocate/free frozen pages for slab already. Once we move the refcount > into "struct folio", they will not have a refcount at all anymore. > > One complication is balloon compaction: we allow for migrating > PageOffline pages allocated in some memory ballooning implementations > such as virtio-balloon. > > For that, we use the "non-lru page migration" framework and in that > process we make use of ... way to many members of "struct page"/"struct > folio" and rely on the refcount not being 0. For example, we certainly > don't want to allocate memdescs for PageOffline pages just so some of > them can be migrated. > > While we converted non-lru page migration to work on folios (i.e., > folio_movable_ops()) these things are not actually "folios" in the > future, they can have different memdescs. > > So, how can we migrate non-lru things that are not folios while not > relying on "struct folio" members, with minimal/no metadata overhead? > > I have some ideas, but no complete solution yet; input about the > requirements of other non-lru page migration use cases besides > PageOffline will be interesting. > > ... and maybe, we have other non-folio things we'd want to migrate, and > want to be prepared to handle them as well? (hint: leaf page tables?) > Slides from today: https://drive.google.com/file/d/1NIjjwVAonz9WWIoJZ0nh71ovMfSjfqFc/view?usp=sharing -- Cheers, David / dhildenb