From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B1DF556E074; Wed, 14 Oct 2026 18:46:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792003594; cv=none; b=mTz4f01+VEGEzQJz1ioR0iprANK4vml2/s00yeLmN0lMi7O2O8iZ4QHTLvk1dd1a46txbG61qQPa6VsxizoX96gWv3YQBErv9AeqKK2m8nlPtjtYbmjnoL82ULHN5Hc137OtuyiRcxSjcZ99VYC+jbdcHxQUSoYgW5BI8ERWVW4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792003594; c=relaxed/simple; bh=QGeni+Dqy7rYyILLSs/q1fCNwL/enmT+EXAbDw7GYOQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Huk1jqPx88ngZGw5iSmzoZXBw39VA9wfBcRWbHH8e1YBQ26V/sCVsL40/WzQIweNa/gjl0aRHcFQrgNIAjIkwhrpwFMv7h9zAguoDm7LqArS26rz969daYoM6ctVYChtEuUbhKtcHfwkpGp1MkEO6aBAxd6vUAEZgfPLyfF6Nzg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Fc1TvbQ/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Fc1TvbQ/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 343281F000C4; Wed, 14 Oct 2026 18:46:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792003593; bh=ESvCGRLFTew8m7s5oFwM1Eu4zFgjax4mVQujOpbznXo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Fc1TvbQ/IoFOWkS4r9GpWZ2uI/Fmq5vGoocDI2qZsvsZOVwo8dmzPHQ9AwpQI65xc 0hyNO9BHNGvfFFpSBYm6orjA9dwMSWtC7ZyO/ycpjw7otwP49fLanDBobCsJVEWMCr V+BY4QuqvYvzydWxhGX/5ZlKzq0/6KndsbuCTpxkdJvRzjdoh7Ew7OQv7F9ut0mcUC BcxLEXSN2DMEcYDt/rzRwnx5zVlXYIKJpbj97Vsl7f/CqzKtaKk7pBlz2sPbF5x/wk GGohatcwUAzO3eKrwCn1+89fS13vuVrYOYYmgOM6V864X5fudq0RjKnemq2o8lEQHh WPSB8j57GDIzQ== Message-ID: Date: Wed, 14 Oct 2026 20:46:19 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Path forward for Virtualized Swap? To: Kairui Song , Chris Li , Baoquan He , Nhat Pham Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Yosry Ahmed , Muchun Song , Kemeng Shi , Barry Song , YoungJun Park , Chengming Zhou , "Lorenzo Stoakes (Oracle)" , "Liam R. Howlett" , "Vlastimil Babka (SUSE)" , Mike Rapoport , =?UTF-8?Q?Suren_Baghdasaryan=EF=BF=BC?= , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , Rik van Riel , Gregory Price , Wenchao Hao , Jonathan Corbet , Hugh Dickins , Baolin Wang , Tejun Heo , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Shuah Khan , Kunwu Chan , Meta kernel team , Linux Memory Management List , Linux Kernel Mailing List , linux-doc@vger.kernel.org, "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , Andrew Morton , Joshua Hahn References: <5fdb3777-95a2-48f9-bb38-aa4ba3c96a81@kernel.org> <5ca344de-bc34-4a9b-ab85-f553811a1d9c@kernel.org> <5c8a2b7b-b76d-4bba-92e1-ec3d66794273@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/14/26 19:17, Kairui Song wrote: > On Tue, Oct 13, 2026 at 1:27 PM Chris Li wrote: >> >> On Mon, Oct 5, 2026 at 5:19 AM David Hildenbrand (Arm) wrote: >>> >>> >>> Looking at the mailing list, that approach doesn't seem to work. >>> >>> Finding a time slot that makes US, Europe and Asia happy is ... tricky. >>> >>> 1 AM is certainly unpleasant. >>> >>> US vs. Asia is also tricky, but doable. >>> >>> China 8AM vs. US West Coast 5PM? >>> >>> China 9AM vs. US West Coast 6PM? >> >> Hi David, >> >> Thanks for organizing this. Time slot that works for Baoquan and >> Kairui should also work for me. > > Let's see Baoquan and other's suggestion, both slot are fine to me as well. > >> >> Hi Kairui, >> >> I understand that you have some face-to-face discussions at the >> conference. Do we have a list of what has been aligned and what is >> pending to discuss? We should have an agenda to avoid repeating >> already aligned items. > > Right, from my perspective, here are the following key points we can > discuss further in the incoming meeting (most of them are not fully > concluded yet): > > 1. A limitation for the logical size: from my side, there are real > usages for a global non-memcg limitation of the non-physical swap > space: e.g. thin VMs as containers/pods with no cgroup limitations > inside but which need in-VM memory compression and a proper limitation > to avoid thrashing; or low-end devices/desktops that want global > (root) limitations. And also, Android have a limitation on the ZRAM > size (well for this one I'm not from Android team though so that's > just my personal development experience with Android, enlarging the > ZRAM size on several Phone swill cause serious junky of Apps due to > over compression). > > Nhat is concerned that exposing the sizing allows users to tune it and > potentially misconfigure the system. However, I think a user with root > permission should be fully aware of what they are doing or they can > easily mess up the system in many ways and swap limitation is a very > minor concern to me. > > I think the requirement for a logical non-cgroup limitation is strong, > but the discussion hasn't concluded on the implementation method. > Perhaps something like a Kconfig combined with an interface or command > line? More ideas are welcome. > > 2. Charging: If you consider memory.swap is physical only then indeed > we should not charge it, however, user are already doing that for > years so this is a behavior change and we are also pushing memsw into > memcgv2 as a interface to limit the logical memory usage of a > container. So charging of the logical space is useful, how to handle > that is tricky though. > > From our usage, this should at least not block adding memsw or > anything similar for memcgv2, even if you want more customized cgroup > accounting, we need to charge it into some counter (a page counter, > not just a statistic) in some way. > > 3. Swapoff: This was discussed again too, as vswap was trying to > remove it. I think the concern is mostly about maintenance, > performance, and practicality. From my perspective it's a critical > component both for preventing minor or major faults before predictable > high traffic arrives, or for operations/debugging, and for releasing > the swap metadata to rule out any potential swap / page fault effect. > There are concerns about maintenance or suggestions to use MADV, while > I'll be happy to explore and improve the current in-kernel > implementation of swapoff later if needed but removing it is a really > bad idea in my view. > > 4. Writeback: No doubt we all agree that we definitely should have > writeback support, Nhat's concern is that we should handle the case > where some cgroup doesn't need zswap/compression and ensure that works > well. > > 5. Interface: Given the issues above, what should the interface look > like (swapfile, sysfs, /proc, etc.) and how should multiple > (non-physical) swapfiles be used? Nothing much is discussed about this > part though. I've heard users mention the use case of multiple > compression swap spaces, but I don't have a use case for that myself, > so I don't have many comments. > > 6. The one part that I think we can and should agree on it shat the > implement approach: at this point I think VM_SPARSE is the right > direction, Nhat is concerned about the testing on it, and I think we > can have more data for that, and collabration is highly encouraged. I > previously conducted many tests on everything posted from both sides, > will try to post more on this too. > > That's a lot of problems already. I think we can discuss these points > further in the meeting. Just in general, if I'm attending and it's 2/3am in the night, I would appreciate a short summary of "these things were already sorted out". I might have some weird swap-related dreams afterwards, but it would certainly help keeping my brain awake. Surprisingly, sometimes summarizing common understandings still sparks discussions ;) -- Cheers, David