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b=HDehqxcoOny8+q9R/EQrECENhPrcPyoKzzgP48p0XVXIeAHZK7kpMVnvB44IoPzBo t6peJordL6ZByfnTUShrHNma+rjCqHTXfn9dvabV+92O0EfkBkI8KUoBKymYSOty0d 0DAxql17MW5mjR1tyRF5NcCKv0QZCAUpwjGe6tslOAClLsNNSGbJ6CB+qQ2vBal5uB +th+LAgu3k/fmOJc1Du1SrOEBn/5tIRmvvsIdh9cXGYHQ35ks0K9D8FMEwuUphn9nQ EJfLzffgxpbdRb43CYfTDmjNKAn9dLdq4RyT8l+6poo9Dk2F5WGu15s/fBUx90mvT6 o0aHe7Qa+VN7Q== Message-ID: Date: Tue, 12 May 2026 08:14:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/5] mm: support zswap-backed anonymous large folio swapin To: Yosry Ahmed , fujunjie Cc: Andrew Morton , Chris Li , Kairui Song , Johannes Weiner , Nhat Pham , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Jonathan Corbet , Ryan Roberts , Barry Song , Baolin Wang , Chengming Zhou , Baoquan He , Lorenzo Stoakes References: 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: 7bit X-Rspam-User: X-Rspamd-Queue-Id: C604540009 X-Rspamd-Server: rspam04 X-Stat-Signature: yjrydd3hd71zscffnbryygconqq3t8na X-HE-Tag: 1778566465-558032 X-HE-Meta: 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 DBAJergr +/pG2g7RmK5pU7w+LxrjitnnE6hlTTeFhDvz8qL9ePY3q2Ldege/RdSpmXMgiuOSUdsrAa2XT6xBOWGmdo1FVMLIgfUm+RexnQVROOi+xyKbxnMN5Lij6X8HmUUS293is6rHcF6S8okEmiix5g442QOmX6kUjiyKZcfbXVX6bgXR8JoZVq51hUUXt+4b8Vtf21sY6MqkpilP43Z3IgC6vMjIgihzqlpa2wYdKswG8rNTL3y6IQ39mVFF5Uysasjrq0VWn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/12/26 00:13, Yosry Ahmed wrote: > On Fri, May 08, 2026 at 08:18:29PM +0000, fujunjie wrote: >> Hi, >> >> This RFC explores anonymous large folio swapin when a contiguous swap >> range is backed consistently by zswap. >> >> Large folio swapout to zswap is already supported by storing each base >> page in the folio as a separate zswap entry. The anonymous synchronous >> swapin path has remained order-0 once zswap has ever been enabled: >> zswap_load() rejected large folios, and alloc_swap_folio() avoided large >> folio allocation to protect against mixed backend ranges. >> >> This RFC keeps the scope intentionally conservative. It does not try to >> read one large folio from mixed zswap and disk backends, and it does not >> change shmem swapin. Shmem still has its existing zswap fallback and is >> left for later discussion. For anonymous swapin, the backend rule is made >> explicit: >> >> - a range fully absent from zswap can keep using the disk backend >> - a range fully present in zswap can be decompressed into a large folio >> - a mixed zswap/non-zswap range falls back to order-0 swapin >> >> The series adds a zswap range query helper, teaches zswap_load() to >> decompress all-zswap large folios one base page at a time, accounts mTHP >> swpin for zswap-loaded large folios, retries synchronous large-folio >> insertion races with order-0 swapin, and removes the anonymous >> zswap-never-enabled restriction once mixed ranges are filtered. >> >> I tested the series with a full bzImage build using CONFIG_ZSWAP=y, >> CONFIG_ZRAM=y, CONFIG_MEMCG=y and CONFIG_THP_SWAP=y. >> >> The QEMU/KVM runs covered both the fully-zswap path and the mixed-backend >> fallback path. In the all-zswap run, a 512MiB anonymous mapping was faulted >> as 8192 64KiB groups, reclaimed into zswap, and faulted back. Reclaim >> reported mthp64_zswpout=8192 and zswpout=131072. Refault then reported >> mthp64_swpin=8192 and zswpin=131072, and pagemap/kpageflags showed 8192 >> order-4 THP groups in the mapping. >> >> In the mixed-backend run, the workload used a 64MiB anonymous mapping >> split into 1024 64KiB groups. After shrinker debugfs wrote back exactly >> one zswap base-page entry, refault left 1023 order-4 THP groups and one >> order-0 mixed group. The kernel stats matched that shape: >> mthp64_swpin=1023, zswpin=16383 and zswpwb=1. >> >> CONFIG_SHRINKER_DEBUG is only a test aid for making that one zswap >> writeback deterministic; it is not required by the implementation. >> >> Nhat Pham's active Virtual Swap Space series is adjacent work. It moves >> swap cache and zswap entry state into a virtual swap descriptor, and lists >> mixed backing THP swapin as a future use case. This RFC is independent and >> works with the current swap/zswap infrastructure, but may need rebasing if >> VSS lands first. >> >> Feedback would be especially helpful on: >> >> 1. whether it makes sense to support all-zswap large folio swapin first, >> while keeping mixed zswap/disk ranges on the order-0 fallback path > > I think so, yes, but based on my read of the code this RFC only affects > synchornous swapin, which is more-or-less zram+zswap. This is an > uncommon setup outside of testing. BLK_FEAT_SYNCHRONOUS is also set for pmem and brd devices I think, but that's also pretty uncommon I assume. Well, maybe if your hypervisor provides you with an emulated NVDIMM to use as swap backend ... maybe. I thought there were other ways to get BLK_FEAT_SYNCHRONOUS set, but I don't see other usage. So seeing it for zswap is pretty rare I assume. -- Cheers, David