From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794316379; b=N40Yn4GBg6fYuXA8zQUpNPWnjN+HKM/Qv7bflL/Gn21QxOx4gnDJiZzdxf1mW8yDyiIj 3dpzblhdEn4bs1AmJfsiUXEOD80hbCXqwVgDI95sMgIUh0ApxaGYjyuGrdMygZL5dFkmM HIGmkwvBn/pZTHNWjrJq3xccfkZFrnW84iVOT0PRdq7JkrSNYvZ0hEUy4BKP7TKtCwdz+ t2gpDN1Bx+A5tRSHqm/aurabs68VjfYLzsSghfZff9XyEDrKNhnS24BNZhDUPTVkLHUrd 3p+LS6k6WZ1L1tJTmPS/4TTDQo9s5i25daH6WY4rqzqU5Zzb9P/5dpn5DX4EWvatXwg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794316379; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=lH5RrpAfhToS5Cr0qmiZUZ/9Gvt2X+LmFZ63KOZlNtw=; b=SzqsJxUxwb1Y+cZWVJ4n4b5MuXUwrYSjBfDb3/MK0gbEQp3lPk5aQ7cPC2Rkn/6Tn0tq gydwGk29h7jNXpn2YbVCnpI9IiZ5W7fArMdBY9TEANHDyKMDItQsBBD3s6eQ2GH7RPDtB hHuTqJHGegpXIS/LvM4Ze1/dqe3oDXgwkSSs9eR0Gcy0v87Nmb3Txb6HwKDG9USajLHbz /6CZCV/MNJ/SuWdRL7vDI1iLr5WXSlglzpT3WOGudvb1Yjjgnz5PVR0gwkJxKCbGWJJ04 OAqTchl9oJD1mg8urQaMpmxukXdUHX25QdTKFlxyuWqJmGptRr5qsTZMQSZIL9zfE1A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=EhfGcWss; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BDA24606A7CF for ; Tue, 10 Nov 2026 13:12:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=EhfGcWss Received: by smtp.kernel.org (Postfix) with ESMTPSA id 66A291F0089F; Tue, 10 Nov 2026 13:12:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794316378; bh=lH5RrpAfhToS5Cr0qmiZUZ/9Gvt2X+LmFZ63KOZlNtw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EhfGcWssm5mwvPcP15MxRq+AxtbzI5vLg4mmjoRb7xKLF3nKLwweK0YB3gC1L78Wp x5UnJlOr1WAqWxD6/lVGjWT7ZjtZRVG5IBBdfWXdvle3UUKQ+/Gy74m7AJBpL03k57 W5eDyuhxwC6legwnJhYuJTiK+l/xpNxK1ub5LJpu32u2uNHF0pPCwZrLS78/jpqIn5 TgZsjd95BLT1oWkyiqlsjuSZduYzdHJbRs855JZQpV05NXWT0tpNngKUFP2eNGCJO2 WWM2VcKzb25WC6D6MnDN+7YyzVxAWqcl0VuLLPSGxQcjFmv/Dc/eoZ2Pb37fXQbEFX SbHt67W0pTjpg== Message-ID: <529b409d-748e-4f47-bb21-77b3237da39f@kernel.org> Date: Tue, 10 Nov 2026 14:09:32 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 6/6] mm: gup: batch PTE-mapped large folios in gup_fast_pte_range() To: Yeoreum Yun , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jason Gunthorpe , John Hubbard , Peter Xu , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Andrew Morton , Rik van Riel , Yuan-Hao Hsu References: <20261109-refactor_gup_fast-v3-0-2aaef02df0e1@arm.com> <20261109-refactor_gup_fast-v3-6-2aaef02df0e1@arm.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: <20261109-refactor_gup_fast-v3-6-2aaef02df0e1@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/9/26 13:32, Yeoreum Yun wrote: > GUP-fast grabs a PTE-mapped large folio one page at a time. Every PTE > costs a try_grab_folio_fast() (a refcount cmpxchg, plus the pincount > atomic, a full barrier and a node stat update for FOLL_PIN), a > gup_fast_folio_allowed() and a folio_set_referenced(), so a 64 kB mTHP > pays sixteen of each and a PTE-mapped 2 MB THP pays 512. > > The users are the hot ones: iov_iter_extract_user_pages() pins every > O_DIRECT buffer through pin_user_pages_fast(), io_uring registers its > buffers through it, and so does RDMA memory registration. > With mTHP those buffers are PTE-mapped large folios. > > After the head page has been grabbed and verified as before, extend the > run to the following PTEs that map the next pages of the same folio > with the same protection bits, take the remaining references for the > run with try_grab_folio(), and fill pages[] from the run. > The PTEs of the run are read while the reference on the folio is held, > so the folio can neither be collapsed, freed nor split underneath the scan. > A read-only run of an anonymous folio stops at the first page > that gup_must_unshare() rejects, so the per-page exclusivity guarantee for > FOLL_PIN is kept. > > folio_pte_batch_flags() does the scan. It reads the entries with > ptep_get(), which is not safe without the page table lock on > CONFIG_GUP_GET_PXX_LOW_HIGH (x86 PAE, mips32, sh) or with arm64 contpte, > and GUP-fast reads every PTE with ptep_get_lockless() for that reason. > Add FPB_LOCKLESS to make the helper do the same; it is inlined per call > site, so the other callers do not change. > > The order-0 path keeps its instruction sequence. The folio flags are > tested before folio_set_referenced() on purpose: a load of the flags > right after that locked instruction cost about 25% on order-0 pages in > the gup_test benchmark below, and reading them first brings that path > back to the baseline. > > gup_test ioctl over a 256 MB anonymous region, FOLL_WRITE, 65536 pages > per call, median of 15 runs, two baseline boots / one patched boot, on > an x86-64 VM: > > get_user_pages_fast() pin_user_pages_fast() > before after before after > 4 kB pages 849/789 us 783 us 1174/1138 us 1094 us > 64 kB mTHP 812/811 us 126 us 1215/1113 us 188 us > 1 MB mTHP 799/774 us 59 us 1185/1077 us 64 us > 2 MB THP, PTE-mapped 803/786 us 57 us 1159/1120 us 58 us > 2 MB THP, PMD-mapped 42/40 us 40 us 46/41 us 42 us > > fio O_DIRECT randread of a null_blk device (CPU bound) with the I/O > buffer in 64 kB mTHP, median of 15 five-second runs: > > bs=1M psync 126.2/125.6 GB/s -> 220.6 GB/s > bs=1M io_uring, iodepth 16 71.2/71.6 GB/s -> 112.1 GB/s > bs=64k io_uring, iodepth 16 50.2/50.7 GB/s -> 60.1 GB/s > > IORING_REGISTER_BUFFERS of 1 GB, median of 15: > > 64 kB mTHP 6179/5998 us -> 1599 us > 1 MB mTHP 5790/5801 us -> 893 us > 4 kB pages 7173/6741 us -> 6763 us > > Signed-off-by: Yuan-Hao Hsu There should likely be a co-developed-by? (also in the other one?) LGTM, thanks. Reviewed-by: David Hildenbrand (Arm) -- Cheers, David