From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5F61AC55822 for ; Wed, 5 Aug 2026 07:36:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 35F656B009D; Wed, 5 Aug 2026 03:36:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3104A6B00A0; Wed, 5 Aug 2026 03:36:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1DB9E6B00A1; Wed, 5 Aug 2026 03:36:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id E1EAE6B009D for ; Wed, 5 Aug 2026 03:36:13 -0400 (EDT) Received: from smtpin02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 5F95A40408 for ; Wed, 5 Aug 2026 07:36:13 +0000 (UTC) X-FDA: 85066407426.02.486A114 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf05.hostedemail.com (Postfix) with ESMTP id A554F100007 for ; Wed, 5 Aug 2026 07:36:11 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="M/SYiQjD"; spf=pass (imf05.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785915371; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=78alTOF1FqEo4Ow5pLyKuZcZuxJN46NIcS9bo25EeB0=; b=ZhNMVYyQJKAtBYWCRVQQuOScnvXP+Y3ADm34wcMuSgbvgg1wy6NfkbdluCsckNx784KOsN v02eAFtBjprXvmeePeTitFD/sKcXoOBZP19dfoj3JfyQMuG1li2iSGpG0CgoJ6DVv19+Da iMxA3D7OZmcCPvz+RV/rFb/12feo980= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="M/SYiQjD"; spf=pass (imf05.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785915371; b=iIsgD3iQgZcdBSESb1UWjvgXCZFfWo/n9hIsZkPPR3OZs2Feqa3o9v4GYEKN1Uk3UyZFVq D2JmOjyssO6vRpJ/XyJWrqVC7f1AKLf2B+9QPIEEB6jM8+2sw0N3EG+euXaRCSNkR09R7k Yc5dNehrgoVI8agDkVTnen1uE8r3nas= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3D2DC60A75; Wed, 5 Aug 2026 07:36:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 056B71F000E9; Wed, 5 Aug 2026 07:35:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785915370; bh=78alTOF1FqEo4Ow5pLyKuZcZuxJN46NIcS9bo25EeB0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=M/SYiQjDmuZSjqnYxXZ95MsY7qnrZNP/2qcBuPFpwww/h3s7augHkh4Qb7sJDNIpI zCJpS8TfaqPSJX9Xkbimbbu/AtEZ+sru5+OWBQ/Dedf7v1HjexBRfOeEGjYJanu+e9 0FsoKGiSNpztorzZoQ7tT92Rw9IG2bagJ/XkKGt25a5weYaV5WtIolvU0wS0Pf5Wba 41KhCSPLcZ5zeMwwlhwHjZgjPl3lz4ZeEsJq6JwFWgNMdZCgehBh8yfliDC3flvjjZ MmnglQoFHz9Nxe56kAKFbywu//t4JOMZ6MCpDyjIDG9R+oiPQqKLA6VC1fCRrf26D9 1xVofBvwKBvPA== Message-ID: <6ea7cdad-afb1-45af-a63c-30b760fe160d@kernel.org> Date: Wed, 5 Aug 2026 09:35:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/15] mm: propagate VMA anonymous page offset on map, remap, split + merge To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260729-b4-scalable-cow-virt-pgoff-v3-0-e8ecfefea812@kernel.org> <20260729-b4-scalable-cow-virt-pgoff-v3-6-e8ecfefea812@kernel.org> <4ad4b17b-bae6-4169-8649-bff4a29e7fde@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: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: A554F100007 X-Stat-Signature: kknkj5s3ggzm5y7fkpg88jg7h47ekym1 X-HE-Tag: 1785915371-718075 X-HE-Meta: U2FsdGVkX19FpLg6EQzNYTWzvHo/k3/0NWtAZWQcp7shNjQ8xk6FMPlAwOy9y+0uFlonsTsqrUVhERGjqjXCrW2aLLdoaqDxDu4gIZnnw6cAP5Hi15AaDf2uDsyzksBEdQpoaICTCBRTB4oxbIYQfqpbGSvEto08DnvDq68O9S2fSGYxPZ01e9yMWU4Z7MNUuiDSOVlrSW/AnmT2hvVGl0xgCMV9NKWJLU6bBd4atmpYphjzJTL9nZQvUuSp5Sr++fSUHLAqa1RhzXesw4kAxrCFF2fvN0aySqNboTt9jAHSoVZSRXQxp8wXGOX8bjGEqMtFLsT7P4ldgE057k1yy0dPytLG7NxEGjyfOGSaShXtasXhyXMQ2eSVkbP0LKuZzMIgYvw0dFqHOc3QzKcjH3ms945dJa2hvYct6nDIELioorAbvocIaSd91XeHPsqBmY5ZtUQYchKLr1ZN9wbax7oY6kr/qKL4/GYQMSvGA7Vu5bS0WtbIhu+YsqBahCbDSYHNZ3m0Y44gHGSf0M1vxWzamqiCONEP88x8Ld8xrxWtTgdc7ZT1f3J6Ey3Q+yVCrWeRcyVFCfJdwOTbiHQvo0ZnDKZRw7PMu8vlG2PZL8jewQNpPZtFmgleqkuL3m+t3o6Z/ZIwT+jeZbCi1O+t6ch+ffMLY7onT77tu9lFTPCrPnhqwMe/9xozbZU4FS76eiYnsKrct+kGQQzcSiK7eLyyWDKadS6Xyer3VAbjmO9zWwIc5kn2IogIqSmvRoAHXbwDBbAzLTnuJPdUiJaducSuTY9qp2LwN0r846KiQ4Hz8LVjiCqfHXlgVUXqD3xBa5JOksZbZXWPizWsP31Us5O8/z4+WKn+/RUji5hCbrJ1KoS6YbMiDqKc50D7hQlHXTaMH0yh6CulYsHeBGM3vQK9PrWolqzNsUucvHGVOYg8scIbkAT4VwikPZYMFR/OHbG4jvGpWcDIvlJcNc9 pWjf8jt0 fE7bYDECKdd38H8uWipju3nhRlWzGRS/kR8Fx7SGqIPMNc1K4DEOEKhlNEtn0CSCXGVN8u9cen6Y8C1he6keoPxbWzW2IP+Yxv4adRe4CvaSs9y68rD/tfoNvagaMXbrLkWUjYPmBhCHuPy942+OLFQhyL1Egrc2tZR5hBab1L8Vj1YvvoAZzZQJfXS97T/KNS26QSUU/q1HskCg5MxTgYFv8rFD0+RniaXS4to8GyRFPLW5rVonOEnWBsA3a9Ihbltfnjs9UdrAkaaAeahooOFBj0cujxqlN+G+NJA/GYXox5VlvIbi4VO077J2ms8C6/PczERXI0kPqHxYoWAU2IiPz5kHOKm2sD7DqkJy8OZLfuOQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/3/26 15:46, Lorenzo Stoakes (ARM) wrote: > On Mon, Aug 03, 2026 at 12:52:42PM +0200, David Hildenbrand (Arm) wrote: >> On 7/29/26 18:48, Lorenzo Stoakes (ARM) wrote: >>> We must correctly update VMA anonymous page offset state on all VMA >>> operations that would result in it changing, with special attention given >>> to remapping. >>> >>> We cover most cases by simply updating vma_set_range() to do so (with a new >>> anonymous page offset parameter), but also notably must update the merging >>> and mapping logic to propagate this parameter correctly. >>> >>> The remap logic remains the same - we may update the anonymous page offset >>> if the VMA is unfaulted, but now this applies to MAP_PRIVATE file-backed >>> mappings too, so we update the code to reflect this. >>> >>> Note that we use __linear_anon_page_index() upon remap as the VMA may be >>> shared, in order that we update the field consistently regardless of VMA >>> type. >>> >>> Similarly, pass through anon page offset to the merge logic, updating the >>> vma_merge_struct struct to propagate it, and also use >>> __linear_anon_page_index() to obtain the anonymous page index so it can be >>> safely used for both shared and MAP_PRIVATE file-backed mappings. >>> >>> Finally, we update insert_vm_struct() to correctly set the anonymous page >>> offset on insertion of a VMA. >>> >>> We simply ensure state is correctly propagated here, so no functional >>> changes are intended. >>> >>> Also while we're here, replace a VM_BUG_ON_VMA() with a >>> VM_WARN_ON_ONCE_VMA(). >>> >>> Also update VMA userland tests to reflect this change. >>> >>> Signed-off-by: Lorenzo Stoakes (ARM) >> >> >> [...] >> >>> struct vm_area_struct *vma = *vmap; >>> unsigned long vma_start = vma->vm_start; >>> @@ -1919,11 +1929,14 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, >>> VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len); >>> >>> /* >>> - * If anonymous vma has not yet been faulted, update new pgoff >>> - * to match new location, to increase its chance of merging. >>> + * If a vma has not yet been faulted, update its anonymous pgoff to >>> + * match the new location to increase its chance of merging. >>> */ >>> - if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) { >>> - pgoff = addr >> PAGE_SHIFT; >>> + if (!vma->anon_vma && !vma_test(vma, VMA_SHARED_BIT)) { >> >> Could we also use is_cow_mapping() ? > > No this would be incorrect. > > A read-only mapping would become unmergeable here. So this is something apart > from the rmap aspect, I'd assume that we should never even consider anon_pgoff when merging !is_cow_mapping(), it doesn't make any sense. No anon folios -> no anon_vma -> no anon_pgoff But I think I am missing one detail here: > and it is a contract that upon move of an unfaulted > mapping (which for read-only anon would always be unfaulted) that vma->vm_pgoff > is updated. "read-only anon": I assume you mean an anon mapping that does not have VM_MAYWRITE set? I recall that that's a combination that cannot be created. While you can create something that does not have VM_WRITE set, IIRC VM_MAYWRITE is always set for anon vmas. -- Cheers, David