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=1793694942; b=5D0GebcAW8O+1dI/d41Y5rAZsq2KRSCpV2hjYKV/NedLY2jV1SCQaYGsOvwE/xg7Kiqo 1V9kx240Nt7DIpMaqtrvQaeuCdIGDUijPDoWPDorwLn4PHO+2cSLCvRrrWaXJetn8lxFK 0TTuAHP9Fy6f7D/5/jDiIRetNNgYhzPD805g7yD8h8GtjG97cdNwS+HVH5LcmFpZmhPuh XB+88tEmZ8ojDIt4IFY7W59rhPRUp+DW3S9YvfGZhgyZovE5zQ4CYCtXikUpAzqnob0M6 I7sbELlaRBKiyjgPm+bjMmeIyVC0lJzIOn1NOD6XLWIDvZpkT6j8hCXu6WXGwjhOmZw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793694942; 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=xLSzO9iZJW/dawul74UtMkV0+UbbhY7vlsAzsGmNnjM=; b=RoPszowPs+/OYV3JvwcA7UwUxDAOjj8dCNxFAU+9bT2nKLAPT6/bUlllubi4nO3bcyb0 fl4uwMINvRFL5gzQl/X/H5ykO7woBkz4SxGPNckDR+4wlDEKyNxjYfDwhQbze3vgpgt3G 2xNhhnhcpv+30pFVxynfL2VomcVceQscHgO18ZNuWqqomTpl08c/p3i6gxDMI+FbnGAzt H7vAwhk1A3B2+uh7eOKIy/t9qgReNE3+7ZfulJDq0B8hc6NRzN1riihhZxdBij5IB9rf2 3OI1pqdNlT75vODLREdJ+6wyIG64w0T4IAkXR7Gf+d3LLjWHNiPRh3Wg9A8ABVbYwNA== 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=IEjH+kwe; 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 9D2B6606A32C for ; Tue, 3 Nov 2026 08:35:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=IEjH+kwe Received: by smtp.kernel.org (Postfix) with ESMTPSA id 96B011F00919; Tue, 3 Nov 2026 08:35:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793694942; bh=xLSzO9iZJW/dawul74UtMkV0+UbbhY7vlsAzsGmNnjM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IEjH+kweDnrDGMvGvPfuOOsJDJfRm7la8rOgwBQPs6ZW4p+I1DS7AWtD3F9EkMAAa hO8KIzaeggQQZ9rhJXPUopHBi+oH/FcU21xL88tsCOn2hTaef2b3wIhOGoxvcv4T2s hxu1FmnrQfImqYACRzwXZSdMlw2y3MZ41Vbx4U/8Bcw2Brp2ziuwZxxdbFSHxVPJJ5 /IlRtQwHMcBihXeJ1bgeDmAGLOIN+ZLnR79gxtMJK8YU7oDb0XxEU+J+Hw0ECEU412 oRiuW27VbE3Jgh+AD/cXh/EMdfTVI5yxRIRxYONSRqomWEaklTiPkntzTzoKdRpzkm fqRnREjbmQKnA== Message-ID: Date: Tue, 3 Nov 2026 09:35:35 +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 8/8] mm/gup: batch contiguous same-folio PTEs into one refcount grab To: Rik van Riel , linux-kernel@vger.kernel.org Cc: Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , Suren Baghdasaryan , Yuan-Hao Hsu , Christoph Hellwig , linux-mm@kvack.org References: <20261102193026.3860700-1-riel@surriel.com> <20261102193026.3860700-9-riel@surriel.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: <20261102193026.3860700-9-riel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/2/26 20:30, Rik van Riel wrote: > follow_page_pte() now walks a whole page table in one call, but still > resolves and commits each PTE on its own, so a PTE-mapped large folio > (mTHP) pays one try_grab_folio() per subpage. > > Add gup_pte_batch_len() and give gup_grab_folio_pages() a run > length. Each run starts with a full per-PTE resolve, then > gup_pte_batch_len() finds how many more PTEs extend it with a pte_same() > scan rather than a re-derivation of each page, and the run is committed > with one refcount grab. Runs stop at folio boundaries, so plain base > pages are unaffected. > > Gather the dirty bits from all the PTEs in a batch, in order to mark > the folio dirty for FOLL_WRITE. > > Same benchmark as the previous change, with before again taken at the > base of the series: > > gup_test -L -m 256 -n 65536 -r 16 -t > before after > 64 kB mTHP 2946 us 231 us (12.8x) > 4 kB base (control) 2753 us 1198 us (2.3x) > 2 MB THP (control) 72 us 71 us > > The 4 kB column is the previous change's 2.3x, unchanged: base pages > share no folio, so there is nothing to batch. 64 kB mTHP goes from that > change's 2.2x to 12.8x, a further 5.9x from committing a run with one > refcount grab instead of one per subpage. > > With FOLL_TOUCH, folio_mark_accessed() runs once per run instead of > once per page: 512 calls before and 32 after over 2 MB of 64 kB > folios, leaving them referenced but inactive after the first call. > That matches the huge-page and fast paths, which mark once > per folio. (Measured by Yuan-Hao Hsu.) > > Suggested-by: David Hildenbrand > Signed-off-by: Rik van Riel > --- > mm/gup.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 46 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 67e20b326be6e..47f204e21a3a7 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -937,6 +937,35 @@ static long gup_lookup_pte(struct vm_area_struct *vma, unsigned long address, > return 0; > } > > +/* > + * Return how many PTEs map consecutive pages of the same folio and can be > + * committed as one run. Always at least 1. > + * > + * The write-fault and unshare checks in gup_lookup_pte() are per PTE, but a > + * writable run needs no repeat: a writable anon page is exclusive. A read-only > + * run under FOLL_WRITE or FOLL_PIN does need the per-page check, so it stays > + * one page at a time. That's a clear indication that this needs more work. I'll try to get to it soon and see how it could be done in a cleaner way, likely it should be based on top of the gup-fast series where we will have helpers to check for required unsharing of multiple PTEs. -- Cheers, David