From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 F18C1296BB6; Mon, 23 Feb 2026 15:27:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771860452; cv=none; b=NteLIt4L1NzGdblHzWIELwCjyAjxtoAK4Fki6y8QzggIg67LGYcI6NN1NxK8uo9tSN9pVDaOfQS3DEmgc/qOMJe5B8sePEXkdb1JFpHR32BPIszZhae/bf5lAz7o7o8UrioRchU/pxuAIC9Rl71Rryc4n5gBmvTGf0y8ZEeGrEs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771860452; c=relaxed/simple; bh=sNIFAxdhsfczXp0u6khA1iIW4G427nJP4aj8xANK8vo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jxHB/oxVYmjcc7OXzJut2SqEVYiHB0N7E9aX7sLe5vjs7buJ/R/SqdmJ1ray+Gz6P0KahFIXAZ567hAztu1aCPAYC4dBJPOQN5KY1bWTmIjshtP6XNlb19JmtiS7BLbFBLT15u3DHE52armJZHObsZPb0tXH8FZjM6YmqZixPmA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RhxvaE8n; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RhxvaE8n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5437C116C6; Mon, 23 Feb 2026 15:27:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771860451; bh=sNIFAxdhsfczXp0u6khA1iIW4G427nJP4aj8xANK8vo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RhxvaE8nn/UMV0eGCQCN6bn3AFU1O7cE1NrNBD8N6is7e063xjThYwogLjKdFJpZD ebgIqwodFIJ+4KeMFIny2fwDvixKBYpFJsgYAQDliELDxoz9p+fhiwfUDbNhkB8waw p8eG9KFgN95UWQsqVzDMKndJgRm5J1xgUKy1IlwS6q1YzHNZb9KJTOSc0uYgJPYNsI 8aW0w51Zw0KGVuipNQgBzopbnZuKVbxGgLCSsqb5fNQkktOVlsRD77I4/XyzyzEss/ qQr0MqF/zzAN2DuA2QWeqREmuBOhDFiqADJhUZua6bZDN5d1kKCZ6XX5SVA4N1gOTO qYsSQ7b5JSZFg== Message-ID: <61e2acbc-d3c7-424a-80da-3c34a593c9ad@kernel.org> Date: Mon, 23 Feb 2026 16:27:09 +0100 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 v1 00/11] Zero page->private when freeing pages To: =?UTF-8?Q?Christian_K=C3=B6nig?= , Christoph Hellwig , Zi Yan Cc: linux-mm@kvack.org, Andrew Morton , linux-erofs@lists.ozlabs.org, linux-block@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Jason Xing , Yushan Zhou , "Masami Hiramatsu (Google)" , Vlastimil Babka , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Huang Rui , Matthew Auld , Matthew Brost , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jens Axboe , Christian Brauner , K Prateek Nayak , Davidlohr Bueso , Eric Sandeen , Greg Kroah-Hartman , =?UTF-8?Q?Arve_Hj=C3=B8nnev=C3=A5g?= , Todd Kjos , Carlos Llamas , Alice Ryhl , Damien Le Moal , Johannes Thumshirn , Dennis Zhou , Tejun Heo , Gao Xiang , Yue Hu , Jeffle Xu , Sandeep Dhavale , Hongbo Li , Chunhai Guo References: <20260223032641.1859381-1-ziy@nvidia.com> <5105764a-8313-45bd-8b91-8c0ea8cdf077@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; format=flowed Content-Transfer-Encoding: 8bit On 2/23/26 16:22, Christian König wrote: > On 2/23/26 15:14, David Hildenbrand (Arm) wrote: >> On 2/23/26 15:06, Christian König wrote: >>> >>> Completely agree. This is just asking for trouble. >>> >>> The cache line(s) backing this struct page are most likely accessed anyway on free/alloc. So I don't see much extra overhead. >> >> I think the question is more around handling non-head pages when freeing larger orders. But maybe the overhead of zeroing page->private it there as well in __free_pages_prepare() is tolerable. > > Good point, sounds like that is a bit more than I thought it would be. Right. We already iterate over all "tail" pages in __free_pages_prepare() to clear page flags (page + i)->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; Maybe zeroing page->private there is not too bad. > >> I'll note, though, that we already require page->mapping and page->memcg_data of pages to be zeroed by the caller, so it's not completely crazy. (see page_expected_state) > > Well that's not defensive at all, basically everybody which forgets to do that can cause hard to debug trouble. Maybe that practice should be reconsidered. Right, we do have check_pages= to activate the page_expected_state() checks, where we will detect such problems. (including the mapcount being -1 etc.) -- Cheers, David