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 4F39D424D73 for ; Thu, 13 Aug 2026 19:35:38 +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=1786649739; cv=none; b=atsUl//UQhY6Cazs/QfL8mERPyvORFlq97PcNLpCsS7jvOzm9E5Rkh3bdvahP9UIWstZSlDcT46jdCAEWakuxFCqyww8PHkWjtqBYsd8qbsNc8FTr2snBxk03m0C82ndCs1wLKAglka53Sk5Xo+bBMd4ypTQM+gyVw1T2ltINuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786649739; c=relaxed/simple; bh=iJ9o4r7HuQm9KQfDHRQIZuxf8njNgMwUdecfnlKcfdo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Zq8WZN1M3KkoE+Rd2wWI9Igns2VGRARyEAxGoJK6QwOQqQ5LRw2gN6Gn0Kw3nfLfldc26LjNlZVEMZKqi+buZMbMWECaNz2s++cyQPTjglBqoUJTEDbB+AahGl30VFN0w9kZ6R6/X3uM8lLPPUFNshgdBQe7A1JMgY5gtojYYSU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=W0JQGfhX; 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="W0JQGfhX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D2CA01F00A3D; Thu, 13 Aug 2026 19:35:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786649738; bh=KEBeBGKqcYmQquziix0FBBLpmC/A5w7ICEtCSGsPqXk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=W0JQGfhXzjm90qZeu1tlAzd1Oqttsv8eo3/eFnoWp0OWvHd/X/HAEECR+rE2O+5We 2RpWF3tcLkDpsWboQEDS39zCqvZS2noyaOd7hrFd2bXLKIIuW6NUDml2VVCgiTsSu8 KtI87LqX6zp3HQWFgwD4lcMmBFxtTe0FpnNWhWzXU61FKACOjcXqAmGdy8zax68y8P /z6YoYEknizUYyxR9d0OcZnJ3obkFLsCGdOt0TlnJknCY7Eku7g0/8G58KlFMxKPR7 zw0mDtEHp2k2fXeufcKL9ecOU2bywIypmlVwr0XoLN2dtwx8VGzGCnccEIbggjZpTv 8e37wsp7x4/Rg== Message-ID: Date: Thu, 13 Aug 2026 21:35:27 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 00/17] mm/huge_memory: clean up folio split and lift swapcache split limits To: kasong@tencent.com, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Shivam Kalra References: <20260813-swap-thp-cleanup-v2-0-d2ee48c6aa49@tencent.com> 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: <20260813-swap-thp-cleanup-v2-0-d2ee48c6aa49@tencent.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/12/26 20:48, Kairui Song via B4 Relay wrote: > This series clean up the split code, add better swap cache split support > for mappingless, large order, uniform and non-uniform split. Generic > performance is on par or slightly better, and stack usage is reduced. > > The swap cache infrastructure can handle non-uniform or high order folio > replace, so there is no reason for either restriction from the THP side. > What stands in the way is the mixed anon/file folio split routine, > which makes lifting the restrictions hard to follow, and it already > carries some buggy or redundant checks. > > So this series cleans up the split path and separates anon and file > splitting into two helpers. The file split path never sees a swap > cache folio, and that is now enforced up front: a folio that is both > in the page cache and the swap cache can only be a shmem folio, which > remains unsupported and is rejected early. That helps to rule out swap > cache handling in that part completely. Only the anon split path > handles swap cache folios, with an anon mapping or mappingless: > either way the splitting is similar, and non-uniform split is > supported as well. > > Order-1 is still forbidden for swap cache splitting. In theory it is > doable for shmem swap cache folios, but a mappingless swap cache > folio cannot currently be told apart from a shmem one, so forbid it > for all swap cache folios for now. > > Testing: > > The in-tree split_huge_page_test selftest (uniform, non-uniform and > in-folio-offset splits of anon and pagecache folios) passes 62/62 on > the patched kernel. > > ftrace function_graph tracing filtered on __folio_split() was used to > compare per-call durations between the base and the patched kernel on > the same x86-64 box (interleaved runs across alternating reboots; > mean +- stddev of the per-run averages, 135 split calls per run): > > base: 24 runs, 69.6 +- 0.7 us per __folio_split() > patched: 26 runs, 68.8 +- 1.3 us per __folio_split() > > The patched kernel is consistently ~1% faster; with this sample > count the difference is outside run-to-run noise. > > On x86-64 with gcc 12 (-fstack-usage), the stack frame of > __folio_split() shrinks from 240 to 96 bytes, and the worst-case > split call chain from ~544 to ~384 (anon) or ~464 (file) bytes. > > Bloat-o-meter shows a tiny growth of huge_memory.o: > before=58419 after=58446, chg +0.05% (+27 bytes). > > Signed-off-by: Kairui Song > --- I might need a bit to get to this; but the merge window is about to open either way so, so this is material for the one afterwards. -- Cheers, David