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 0F6CB32AADE; Fri, 17 Apr 2026 11:50:58 +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=1776426659; cv=none; b=SA3YRuPXou0R8+thOyNcwoio1VIEiEi/HHrp3IioPZjMedn5S7uqCkUyTQG1J7zGx0Mko8bmG6lAkoGvKJe/fJI4ug/xCCzL4R6X+L63DylZjikRUeGLiNIP639qt324P2HaRdyLYMEk+XQ90jDjpoa8/zBjPDXFxkC7lEWrQ2Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776426659; c=relaxed/simple; bh=eChbAgykxjX0W5rYjX38q+EpgtcI2CThnTHQSgO+2C8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GTbrDUIodZryAVMQMPY/CL0coJ2A3D7v7uvkIlaTQPskKwXIocKiH+Gni3xnIYKL9TaCK0HjnzcoyVu0q7bZz8FJlGaIpMdDPk1IL1DITJv2WFYG+DhKbKnO92MdN0vty1pIpEBjhIDwlZCooXmEhm3pSpEfCx/Ow+TtuhsjQVE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SlAhKPap; 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="SlAhKPap" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67F00C19425; Fri, 17 Apr 2026 11:50:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776426658; bh=eChbAgykxjX0W5rYjX38q+EpgtcI2CThnTHQSgO+2C8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SlAhKPapXV3MGVCHn44BXiJ4tHz78BdMc1lyfrOGcjqzwRPmD1Hc3rHm7p1TxaBRk PQ++dEY3fDb7DCQ4mUa5IvWEqtKLP31N60Ysd2Tt2gAY2LsLyw9MpSp02SY3733zLd MZko1FyQgkrc2bADXrdz8I92E3NKO02cC+yBAXrQVng6/zVdCc4yX4CpJYZsxv1J5Q WRFHqWyBUZvKeZA5Ipu35Yc3XiFyjNj1QLXDIya+la75QzfBjJosdmznj0Z0pTgt5y Wgd8VPKql4RexoTD3gyzmSul528C3LMQKtqg2Vc+Ns0eke9xlBVII8I1VgjrehhiQM g9agWd2ZFrkkA== Message-ID: <2c0f57b1-7a4f-4e50-9d7f-6b96c0f73796@kernel.org> Date: Fri, 17 Apr 2026 13:50:49 +0200 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7.2 v2 02/12] mm/khugepaged: add folio dirty check after try_to_unmap_flush() To: Zi Yan Cc: "Matthew Wilcox (Oracle)" , Song Liu , Chris Mason , David Sterba , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20260413192030.3275825-1-ziy@nvidia.com> <20260413192030.3275825-3-ziy@nvidia.com> <10aadfeb-86c6-47b2-b6ab-b86657aafb88@kernel.org> <842D3AD2-32A0-41E1-AC09-08EC793EAF7F@nvidia.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/17/26 04:09, Zi Yan wrote: > On 14 Apr 2026, at 11:55, Zi Yan wrote: > >> On 14 Apr 2026, at 6:38, David Hildenbrand (Arm) wrote: >> >>> >>> maybe simplify to "folios, since that would require taking the folio lock first." >> >> Sure. >> >>> >>> >>> >>> IIRC, after successful try_to_unmap() the PTE dirty bit would be synced to the >>> folio. That's what you care about, not about any stale TLB entries. >> >> Right. I missed the PTE dirty bit to folio dirtiness part. >> >>> >>> The important part is that the >>> >>> So can't we simply test for dirty folios after the refcount check (where >>> we made sure the folio is no longer mapped)? >>> >> >> I think so. > > After more thoughts, this still works but the reasoning is more complicated. > > After try_to_unmap(), PTE dirty bit is transferred to folio dirty flag if exists. > The code bails out if the folio is dirty. A clean folio means the removed > PTEs were clean, thus TLB entries caching these PTEs have dirty bit not set. Right. > Any write to the folio after try_to_unmap() causes a page table walk and > a page fault due to invalid PTEs, and they cannot proceed since collapse_file() > is holding the folio lock. Right. > As a result, we can skip marking folio dirty > after the collapse. Exactly. > > If we allow a dirty folio after try_to_unmap(), we need to mark the folio dirty > after the collapse like shmem. And a potential optimization is that we only > mark the after-collapse folio dirty if any old folio is dirty after try_to_unmap(). That was my thinking as well, but it would be something we'd try to handle separately. Folios that are under writeback cannot be collapsed IIUC. -- Cheers, David