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[79.242.60.81]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436e2da6271sm32037355e9.9.2025.01.08.12.36.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jan 2025 12:36:45 -0800 (PST) Message-ID: <85e2b81d-9255-4c54-b4ae-de52b2c02e7f@redhat.com> Date: Wed, 8 Jan 2025 21:36:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Swap Min Odrer To: Daniel Gomez Cc: Ryan Roberts , Barry Song , Andrew Morton , linux-mm@kvack.org, Luis Chamberlain , Pankaj Raghav , chrisl@kernel.org, David Rientjes References: <20250107094347.l37isnk3w2nmpx2i@AALNPWDAGOMEZ1.aal.scsc.local> <20250107122931.qpkn43yvs4kq3twi@AALNPWDAGOMEZ1.aal.scsc.local> <470be5fa-97d6-4045-a855-5332d3a46443@redhat.com> <20250108141406.3gen6dnlb3b4zga6@AALNPWDAGOMEZ1.aal.scsc.local> 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: <20250108141406.3gen6dnlb3b4zga6@AALNPWDAGOMEZ1.aal.scsc.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: u-gxH2NylIvG2O5GnxUgtYcMhRAewHYKcMfff89mv4k_1736368607 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: E712B40012 X-Stat-Signature: mbq8ghncnmmt3iwxosyp6jd86x5gnzp7 X-Rspam-User: X-HE-Tag: 1736368611-35415 X-HE-Meta: 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 ofqxocbc kDjqZD803r+YTdUiRJ+R6sJ8+hDmRRz5l7GWrS8mvd/5iKD64V+QXw4KlFr40+bWMrGi18wgsZGFdqRJgpM9RLmuAMMIq9W7S5RgrnBnIvF580afhFTZ62FSABBiCgJmgiySpq1UjvAFKvWMPdzKfuCiankx1s0rc1bL0ZNJt/p5uvbrUa6t1BqDmEh+BKgeVDHXBO/YDz4A71lMEmCY0hHVipYOJ/GPvaOn/BkzlFwDPoeIapJRdWwGnP8qahWMGNcw/oxplTs+GiHs7qWlQqJvB1hCABorMLHmr+y7yq4QFGddYxnsKXt/hCr4abIJW/rGCcm+ONjZtorAssNnM2AO9tI0j1sl1vxnP25JgNscv0RQiOQiH6B9cEBeqG50EL2H4VBbH9k2kvVHVTX6CbjZhhyTjdgQPOLtt 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: >> Maybe the swapcache could somehow abstract that? We currently have the swap >> slot allocator, that assigns slots to pages. >> >> Assuming we have a 16 KiB BS but a 4 KiB page, we might have various options >> to explore. >> >> For example, we could size swap slots 16 KiB, and assign even 4 KiB pages a >> single slot. This would waste swap space with small folios, that would go >> away with large folios. > > So batching order-0 folios in bigger slots that match the FS BS (e.g. 16 > KiB) to perform disk writes, right? Batching might be one idea, but the first idea I raised here would be that the swap slot size will match the BS (e.g., 16 KiB) and contain at most one folio. So a order-0 folio would get a single slot assigned and effectively "waste" 12 KiB of disk space. An order-2 folio would get a single slot assigned and not waste any memory. An order-3 folio would get two slots assigned etc. (similar to how it is done today for non-order-0 folios) So the penalty for using small folios would be more wasted disk space on such devices. Can we also assign different orders > to the same slot? I guess yes. And can we batch folios while keeping alignment to the > BS (IU)? I assume with "batching" you would mean that we could actually have multiple folios inside a single BS, like up to 4 order-0 folios in a single 16 KiB block? That might be one way of doing it, although I suspect this can get a bit complicated. IIUC, we can perform 4 KiB read/write, but we must only have a single write per block, because otherwise we might get the RMW problems, correct? Then, maybe a mechanism to guarantee that only a single swap writeback within a BS can happen at one point in time might also be an alternative. > >> >> If we stick to 4 KiB swap slots, maybe pageout() could be taught to >> effectively writeback "everything" residing in the relevant swap slots that >> span a BS? >> >> I recall there was a discussion about atomic writes involving multiple >> pages, and how it is hard. Maybe with swaping it is "easier"? Absolutely no >> expert on that, unfortunately. Hoping Chris has some ideas. > > Not sure about the discussion but I guess the main concern for atomic > and swaping is the alignment and the questions I raised above. Yes, I think that's similar. > >> >> >>> >>>> >>>> I recall that we have been talking about a better swap abstraction for years >>>> :) >>> >>> Adding Chris Li to the cc list in case he has more input. >>> >>>> >>>> Might be a good topic for LSF/MM (might or might not be a better place than >>>> the MM alignment session). >>> >>> Both options work for me. LSF/MM is in 12 weeks so, having a previous >>> session would be great. >> >> Both work for me. > > Can we start by scheduling this topic for the next available MM session? > Would be great to get initial feedback/thoughts/concerns, etc while we > keep this thread going on. Yeah, it would probably great to present the problem and the exact constraints we have (e.g., things stupid me asks above regarding actual sizes in which we can perform reads and writes), so we can discuss possible solutions. @David R., is the slot in two weeks already taken? -- Cheers, David / dhildenb