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 4AD322DC357; Wed, 1 Apr 2026 14:35:23 +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=1775054123; cv=none; b=Kz6O5o6TCTC0Zlkov2ckslbf01ztqSgRjg/IEHm8L1CwG2ivwO6wYoCv73J2xxI+bKHRyfHGb/dbA4A3afNpTD7y72+puNGEnYZxohDRcdQwboK5bZVZa7ylp7GHage2v9CBRC1oXmr8YNDGBXRxCnn/UPP9oGcIIkXybOHQ200= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775054123; c=relaxed/simple; bh=8L15mk7uBbIcb7Tq2K1XChKVrDaUFFZb9Sv7JfqIHto=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J2PHqVqzMVmu8yN7TAuBHg8jMWuyztHYhva9R4gkKhhrX8pKIDEeOEzXdppWmLTjWDKK8qMC+46/RWd2Y0ZgTQ8NdRYgTpl1GntWekbi24TW38huxXCPFogeDSG1xWhSGrdNOG8XZb5wnYAZL6HBLNZYkJXbGtpyDFJqFqooU00= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YJJhGtI9; 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="YJJhGtI9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8489C4CEF7; Wed, 1 Apr 2026 14:35:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775054122; bh=8L15mk7uBbIcb7Tq2K1XChKVrDaUFFZb9Sv7JfqIHto=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=YJJhGtI9LqaXWQGbRVZsPCUbXFlAgkfoX4ONmNboth4EOEPZ/BavQQ76K3894U6UB o4e7o4BAATRZ8R3zHDRokeuqDK+++QlmsrEtiFtENF3l6Xr4yce6xsquadb55zT+ZV S3QgbVdUGD2S+OTVwVxuRaB0p98IpDkit7XG2XsPRkTcGWwzN6/Cvyrys7jiHKpTrJ zZr1KX1PsRCo+vzPxmj9IolWPJMLgx5+x3O9Jtm3i82jP5VrpwOR/r0f4kOl27syp/ DUaRPDO008259oUk3rrNfXm5o8c8cwGeOFbDTrwdQKVIPjt3mFJ5J9Nu1wr+ANUAqb w/mSd6j0BrhxQ== Message-ID: Date: Wed, 1 Apr 2026 16:35:14 +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 v1 03/10] mm: fs: remove filemap_nr_thps*() functions and their users To: Zi Yan , "Lorenzo Stoakes (Oracle)" Cc: "Matthew Wilcox (Oracle)" , Song Liu , Chris Mason , David Sterba , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , 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: <20260327014255.2058916-1-ziy@nvidia.com> <20260327014255.2058916-4-ziy@nvidia.com> <53cf6157-58b1-4539-a276-2486e8796c57@lucifer.local> <25899F67-955D-44DC-935E-D7F234BD335A@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: <25899F67-955D-44DC-935E-D7F234BD335A@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/27/26 16:05, Zi Yan wrote: > On 27 Mar 2026, at 10:23, Lorenzo Stoakes (Oracle) wrote: > >> On Fri, Mar 27, 2026 at 02:58:12PM +0100, David Hildenbrand (Arm) wrote: >>> >>> There could now be a race between collapsing and the file getting opened >>> r/w. >>> >>> Are we sure that all code can really deal with that? >>> >>> IOW, "they already had to handle it separately" -- is that true? >>> khugepaged would have never collapse in writable files, so I wonder if >>> all code paths are prepared for that. >> >> OK I guess I overlooked a part of this code... :) see below. >> >> This is fine and would be a no-op anyway >> >> - if (f->f_mode & FMODE_WRITE) { >> - /* >> - * Depends on full fence from get_write_access() to synchronize >> - * against collapse_file() regarding i_writecount and nr_thps >> - * updates. Ensures subsequent insertion of THPs into the page >> - * cache will fail. >> - */ >> - if (filemap_nr_thps(inode->i_mapping)) { >> >> But this: >> >> - if (!is_shmem) { >> - filemap_nr_thps_inc(mapping); >> - /* >> - * Paired with the fence in do_dentry_open() -> get_write_access() >> - * to ensure i_writecount is up to date and the update to nr_thps >> - * is visible. Ensures the page cache will be truncated if the >> - * file is opened writable. >> - */ >> - smp_mb(); >> >> We can drop barrier >> >> - if (inode_is_open_for_write(mapping->host)) { >> - result = SCAN_FAIL; >> >> But this is a functional change! >> >> Yup missed this. > > But I added > > + if (!is_shmem && inode_is_open_for_write(mapping->host)) > + result = SCAN_FAIL; > > That keeps the original bail out, right? Independent of that, are we sure that the possible race we allow is ok? -- Cheers, David