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 5554B3E51CB; Wed, 5 Aug 2026 07:36:11 +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=1785915372; cv=none; b=VSZcRUUulGCqhrZnUOTUXXc1pPRlUU+t1XJahLgumus5ncJ6t8+8oUqTXVPk62FlBFHpsmSg6YV0NWppvwSQiu2NOP8QszUDdvcxZhqDvcozcVvg6NUBnXewMtVjqykqHu/0YW3mcvsoVNEo4/8IjKfQfoePZ4kBJam9Kz24sg4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785915372; c=relaxed/simple; bh=5efCkzrWgO2ljY/PhhQ7MxFhBGN8K+dxROkABlEQW4A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iZn/tVOx+Gb75YrTVzkyTyQSpGYgQ/3E5LEjIVFBmVufMRiWKcL/hgciRAHmm2xrVCP9xyHCDSX8a74bXWmyKX/i/kaNIHV4Coth7ZYCR3ZYQQU6EFZmc7Jl4txj2gbzRYALmHWMufVRI2jPmPeP+XgCaE340PKe3htqHsUyLMM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=M/SYiQjD; 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="M/SYiQjD" 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 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 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 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